You are given a matrix consisting of digits zero and one, its size is n × m. You are allowed to rearrange its rows. What is the maximum area of the submatrix that only consists of ones and can be obtained in the given problem by the described operations?

Let's assume that the rows of matrix a are numbered from 1 to n from top to bottom and the columns are numbered from 1 to m from left to right. A matrix cell on the intersection of the i-th row and the j-th column can be represented as (i, j). Formally, a submatrix of matrix a is a group of four integers d, u, l, r (1 ≤ d ≤ u ≤ n; 1 ≤ l ≤ r ≤ m). We will assume that the submatrix contains cells (i, j) (d ≤ i ≤ u; l ≤ j ≤ r). The area of the submatrix is the number of cells it contains.

Input

The first line contains two integers n and m (1 ≤ n, m ≤ 5000). Next n lines contain m characters each — matrix a. Matrix a only contains characters: "0" and "1". Note that the elements of the matrix follow without any spaces in the lines.

Output

Print a single integer — the area of the maximum obtained submatrix. If we cannot obtain a matrix of numbers one, print 0.

Examples

Input

1 1
1


Output

1


Input

2 2
10
11


Output

2


Input

4 3
100
011
000
101


Output

2
import java.io.*;
import java.util.*;
import java.math.*;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class MaximumSubmatrix2 {
    public static void main(String[] args) throws IOException {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskA solver = new TaskA();
        solver.solve(1, in, out);
        out.close();
    }
    static class TaskA {
        long mod = (long)1e9 + 7;
        public void solve(int testNumber, InputReader in, PrintWriter out) throws IOException {
            while(testNumber-->0){
            	int n = in.nextInt();
            	int m = in.nextInt();
            	String[] s = new String[n];
            	for(int i=0;i<n;i++)
            		s[i] = in.next();
            	int count[][] = new int[n][m];
            	for(int i=0;i<n;i++){
            		int c = 0;
            		for(int j=0;j<m;j++){
            			if(s[i].charAt(j) == '0')
            				c = 0;
            			else
            				c++;
            			count[i][j] = c;
            		}
            	}
            	int max = 0;
            	for(int j=0;j<m;j++){
            		int b[] = new int[n];
            		for(int i=0;i<n;i++)
            			b[i] = count[i][j];
            		Arrays.sort(b);
            		for(int i=0;i<n;i++){
            			max = Math.max(max , b[i]*(n-i));
            		}
            	}
            	out.println(max);
            	// print2d(count , out);
            }
        }
        public long count(long index , long value){
        	long end = value;
        	long start = Math.max(0 , value - index);
        	long ans = end*(end+1)/2 - start*(start+1)/2;
        	return ans;
        }
        public void print1d(int a[] , PrintWriter out){
        	for(int i=0;i<a.length;i++)
        		out.print(a[i] + " ");
        	out.println();
        }
        public void print2d(int a[][] , PrintWriter out){
            for(int i=0;i<a.length;i++){
                for(int j=0;j<a[i].length;j++)
                    out.print(a[i][j] + " ");
                out.println();
            }
            out.println();
        }
        public void sieve(int a[]){
            a[0] = a[1] = 1;
            int i;
            for(i=2;i*i<=a.length;i++){
                if(a[i] != 0)
                    continue;
                a[i] = i;
                for(int k = (i)*(i);k<a.length;k+=i){
                    if(a[k] != 0)
                        continue;
                    a[k] = i;
                }
            }
        }
        public int [][] matrixExpo(int c[][] , int n){
            int a[][] = new int[c.length][c[0].length];
            int b[][] = new int[a.length][a[0].length];
            for(int i=0;i<c.length;i++)
                for(int j=0;j<c[0].length;j++)
                    a[i][j] = c[i][j];
            for(int i=0;i<a.length;i++)
                b[i][i] = 1;
            while(n!=1){
                if(n%2 == 1){
                    b = matrixMultiply(a , a);
                    n--;
                }
                a = matrixMultiply(a , a);
                n/=2;
            }
            return matrixMultiply(a , b);
        }
        public int [][] matrixMultiply(int a[][] , int b[][]){
            int r1 = a.length;
            int c1 = a[0].length;
            int c2 = b[0].length;
            int c[][] = new int[r1][c2];
            for(int i=0;i<r1;i++){
                for(int j=0;j<c2;j++){
                    for(int k=0;k<c1;k++)
                        c[i][j] += a[i][k]*b[k][j];
                }
            }
            return c;
        }
        public long nCrPFermet(int n , int r , long p){
            if(r==0)
                return 1l;
            long fact[] = new long[n+1];
            fact[0] = 1;
            for(int i=1;i<=n;i++)
                fact[i] = (i*fact[i-1])%p;
            long modInverseR = pow(fact[r] , p-2 , p);
            long modInverseNR = pow(fact[n-r] , p-2 , p);
            long w = (((fact[n]*modInverseR)%p)*modInverseNR)%p;
            return w;
        }
        public long pow(long a, long b, long m) {
            a %= m;
            long res = 1;
            while (b > 0) {
                long x = b&1;
                if (x == 1)
                    res = res * a % m;
                a = a * a % m;
                b >>= 1;
            }
            return res;
        }
        public long pow(long a, long b) {
            long res = 1;
            while (b > 0) {
                long x = b&1;
                if (x == 1)
                    res = res * a;
                a = a * a;
                b >>= 1;
            }
            return res;
        }
        public void swap(int a[] , int p1 , int p2){
            int x = a[p1];
            a[p1] = a[p2];
            a[p2] = x;
        }
        public void sortedArrayToBST(TreeSet<Integer> a , int start, int end) { 
            if (start > end) {
                return;
            }
            int mid = (start + end) / 2;
            a.add(mid);
            sortedArrayToBST(a, start, mid - 1);
            sortedArrayToBST(a, mid + 1, end); 
        }
        class Combine{
            int value;
            int delete;
            Combine(int val , int delete){
                this.value = val;
                this.delete = delete;
            }
        }
        class Sort2 implements Comparator<Combine>{
            public int compare(Combine a , Combine b){
                if(a.value > b.value)
                    return 1;
                else if(a.value == b.value && a.delete>b.delete)
                    return 1;
                else if(a.value == b.value && a.delete == b.delete)
                    return 0;
                return -1;
            }
        }
        public int lowerLastBound(ArrayList<Integer> a , int x){
            int l = 0;
            int r = a.size()-1;
            if(a.get(l)>=x)
                return -1;
            if(a.get(r)<x)
                return r;
            int mid = -1;
            while(l<=r){
                mid = (l+r)/2;
                if(a.get(mid) == x && a.get(mid-1)<x)
                    return mid-1;
                else if(a.get(mid)>=x)
                    r = mid-1;
                else if(a.get(mid)<x && a.get(mid+1)>=x)
                    return mid;
                else if(a.get(mid)<x && a.get(mid+1)<x)
                    l = mid+1;
            }
            return mid;
        }
        public int upperFirstBound(ArrayList<Integer> a , Integer x){
            int l = 0;
            int r = a.size()-1;
            if(a.get(l)>x)
                return l;
            if(a.get(r)<=x)
                return r+1;
            int mid = -1;
            while(l<=r){
                mid = (l+r)/2;
                if(a.get(mid) == x && a.get(mid+1)>x)
                    return mid+1;
                else if(a.get(mid)<=x)
                    l = mid+1;
                else if(a.get(mid)>x && a.get(mid-1)<=x)
                    return mid;
                else if(a.get(mid)>x && a.get(mid-1)>x)
                    r = mid-1;
            }
            return mid;
        }
        public int lowerLastBound(int a[] , int x){
            int l = 0;
            int r = a.length-1;
            if(a[l]>=x)
                return -1;
            if(a[r]<x)
                return r;
            int mid = -1;
            while(l<=r){
                mid = (l+r)/2;
                if(a[mid] == x && a[mid-1]<x)
                    return mid-1;
                else if(a[mid]>=x)
                    r = mid-1;
                else if(a[mid]<x && a[mid+1]>=x)
                    return mid;
                else if(a[mid]<x && a[mid+1]<x)
                    l = mid+1;
            }
            return mid;
        }
        public int upperFirstBound(int a[] , int x){
            int l = 0;
            int r = a.length-1;
            if(a[l]>x)
                return l;
            if(a[r]<=x)
                return r+1;
            int mid = -1;
            while(l<=r){
                mid = (l+r)/2;
                if(a[mid] == x && a[mid+1]>x)
                    return mid+1;
                else if(a[mid]<=x)
                    l = mid+1;
                else if(a[mid]>x && a[mid-1]<=x)
                    return mid;
                else if(a[mid]>x && a[mid-1]>x)
                    r = mid-1;
            }
            return mid;
        }
        public long log(float number , int base){
            return (long) Math.floor((Math.log(number) / Math.log(base)));
        }
        public long gcd(long a , long b){
            if(a<b){
                long c = b;
                b = a;
                a = c;
            }
            if(b == 0)
                return a;
            return gcd(b , a%b);
        }
        public long[] gcdEx(long p, long q) {
            if (q == 0)
                return new long[] { p, 1, 0 };
            long[] vals = gcdEx(q, p % q);
            long d = vals[0];
            long a = vals[2];
            long b = vals[1] - (p / q) * vals[2];
            // 0->gcd 1->xValue 2->yValue
            return new long[] { d, a, b };
        }
        public void sievePhi(int a[]){
            a[0] = 0;
            a[1] = 1;
            for(int i=2;i<a.length;i++)
                a[i] = i-1;
            for(int i=2;i<a.length;i++)
                for(int j = 2*i;j<a.length;j+=i)
                    a[j] -= a[i];
        }
        public void lcmSum(long a[]){
        	int sievePhi[] = new int[(int)1e6 + 1];
        	sievePhi(sievePhi);
        	a[0] = 0;
        	for(int i=1;i<a.length;i++)
        		for(int j = i;j<a.length;j+=i)
        			a[j] += (long)i*sievePhi[i];
        }
        static class AVLTree{
            Node root;
            public AVLTree(){
                this.root = null;
            }
            public int height(Node n){
                return (n == null ? 0 : n.height);
            }
            public int getBalance(Node n){
                return (n == null ? 0 : height(n.left) - height(n.right));
            }
            public Node rotateRight(Node a){
                Node b = a.left;
                Node br = b.right;

                a.lSum -= b.lSum;
                a.lCount -= b.lCount;
                
                b.rSum += a.rSum;
                b.rCount += a.rCount;
                
                b.right = a;
                a.left = br;
                
                a.height = 1 + Math.max(height(a.left) , height(a.right));
                b.height = 1 + Math.max(height(b.left) , height(b.right));
                return b;
            }
            public Node rotateLeft(Node a){
                Node b = a.right;
                Node bl = b.left;
                
                a.rSum -= b.rSum;
                a.rCount -= b.rCount;
                
                b.lSum += a.lSum;
                b.lCount += a.lCount;
                
                b.left = a;
                a.right = bl;
                
                a.height = 1 + Math.max(height(a.left) , height(a.right));
                b.height = 1 + Math.max(height(b.left) , height(b.right));
                return b;
            }
            public Node insert(Node root , long value){
                if(root == null){
                    return new Node(value);
                }
                if(value<=root.value){
                    root.lCount++;
                    root.lSum += value;
                    root.left =  insert(root.left , value);
                }
                if(value>root.value){
                    root.rCount++;
                    root.rSum += value;
                    root.right = insert(root.right , value);
                }
                // updating the height of the root
                root.height = 1 + Math.max(height(root.left) , height(root.right));
                int balance = getBalance(root);

                //ll
                if(balance>1 && value<=root.left.value)
                    return rotateRight(root);
                //rr
                if(balance<-1 && value>root.right.value)
                    return rotateLeft(root);
                //lr
                if(balance>1 && value>root.left.value){
                    root.left = rotateLeft(root.left);
                    return rotateRight(root);
                }
                //rl
                if(balance<-1 && value<=root.right.value){
                    root.right = rotateRight(root.right);
                    return rotateLeft(root);
                }
                return root;
            }
            public void insertElement(long value){
                this.root = insert(root , value);
            }
            public int getElementLessThanK(long k){
                int count = 0;
                Node temp = root;
                while(temp!=null){
                    if(temp.value == k){
                        if(temp.left == null || temp.left.value<k){
                            count += temp.lCount;
                            return count-1;
                        }
                        else
                            temp = temp.left;
                    }
                    else if(temp.value>k){
                        temp = temp.left;
                    }
                    else{
                        count += temp.lCount;
                        temp = temp.right;
                    }
                }
                return count;
            }
            public void inorder(Node root , PrintWriter out){
                Node temp = root;
                if(temp!=null){
                    inorder(temp.left , out);
                    out.println(temp.value + " " + temp.lCount + " " + temp.rCount);
                    inorder(temp.right , out);
                }
            }
        }
        static class Node{
            long value;
            long lCount , rCount;
            long lSum , rSum;
            Node left , right;
            int height;
            public Node(long value){
                this.value = value;
                left = null;
                right = null;
                lCount = 1;
                rCount = 1;
                lSum = value;
                rSum = value;
                height = 1;
            }
        }
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
}
