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.*;


public class Myclass {
     public static ArrayList a[]=new ArrayList[3000001];
     public static boolean isPrime[]=new boolean [1000001];
     public static Vector<Integer>v=new Vector<>();
     static void pre() {
    	 Arrays.fill(isPrime, true);
    	 isPrime[0]=false;
    	 isPrime[1]=false;
    	 for(int i=2;i*i<=1e6;i++) {
    		 if(isPrime[i]) {
    			 for(int j=2*i;j<=1e6;j+=i) {
    				 isPrime[j]=false;
    			 }
    		 }
    	 }
    	
     }
     public static void main(String[] args) throws FileNotFoundException
    {
    	InputReader in=new InputReader(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int n=in.nextInt();
        int m=in.nextInt();
        char a[][]=new char[n][m];
        for(int i=0;i<n;i++) {
        	a[i]=in.nextLine().toCharArray();
        }
        int pre[][]=new int[n+1][m+1];
        for(int i=0;i<n;i++) {
        	for(int j=m-1;j>=0;j--) {
        		if(a[i][j]=='1')
        			pre[i][j]=(pre[i][j+1]+1);
        		else
        			pre[i][j]=0;
        	}
        }
        long dp[][]=new long[m+1][m+1]; //  idx -- len
        for(int i=0;i<n;i++) {
        	for(int j=0;j<m;j++) {
        		dp[j][pre[i][j]]++;
        	}
        }
        for(int i=0;i<m;i++) {
        	for(int j=m-1;j>0;j--) {
        		dp[i][j]+=dp[i][j+1];
        	}
        }
        long ans=0;
        for(int i=0;i<m;i++) {
        	for(int j=1;j<=m;j++) {
        		ans=Math.max(ans, dp[i][j]*j);
        	}
        }
        pw.println(ans);
        pw.flush();
        pw.close();

        
        
    }
    private static void debug(Object... o) {
        System.out.println(Arrays.deepToString(o));
    }
   static class InputReader 
        {
        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar, snumChars;
        private SpaceCharFilter filter;
 
        public InputReader(InputStream stream) 
        { 
            this.stream = stream;
        }
        public int snext() 
        {
            if (snumChars == -1)
                throw new InputMismatchException();
            if (curChar >= snumChars) 
            {
                curChar = 0;
                try 
                {
                    snumChars = stream.read(buf);
                } 
                
                catch (IOException e) 
                {
                    throw new InputMismatchException();
                }
                
                if (snumChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }
 
        public int nextInt() 
        {
            int c = snext();
            while (isSpaceChar(c)) 
            {
                c = snext();
            }
            int sgn = 1;
            if (c == '-')
            {
                sgn = -1;
                c = snext();
            }
            int res = 0;
            do 
            {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
            return res * sgn;
        }
 
        public long nextLong()
        {
            int c = snext();
            while (isSpaceChar(c)) 
            {
                c = snext();
            }
            int sgn = 1;
            if (c == '-') 
            {
                sgn = -1;
                c = snext();
            }
            long res = 0;
            do 
            {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
            return res * sgn;
        }
 
        public int[] nextIntArray(int n) 
        {
            int a[] = new int[n];
            for (int i = 0; i < n; i++) 
            {
                a[i] = nextInt();
            }
            return a;
        }
        static class tri implements Comparable<tri> {
            int p, c, l;
 
            tri(int p, int c, int l) {
                this.p = p;
                this.c = c;
                this.l = l;
            }
 
            public int compareTo(tri o) {
                return Integer.compare(l, o.l);
            }
        }
 
        public String readString()
        {
            int c = snext();
            while (isSpaceChar(c)) 
            {
                c = snext();
            }
            StringBuilder res = new StringBuilder();
            do 
            {
                res.appendCodePoint(c);
                c = snext();
            } while (!isSpaceChar(c));
            return res.toString();
        }
 
        public String nextLine() 
        {
            int c = snext();
            while (isSpaceChar(c))
                c = snext();
            StringBuilder res = new StringBuilder();
            do 
            {
                res.appendCodePoint(c);
                c = snext();
            } while (!isEndOfLine(c));
            return res.toString();
        }
 
        public boolean isSpaceChar(int c) 
        {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
 
        private boolean isEndOfLine(int c) 
        {
            return c == '\n' || c == '\r' || c == -1;
        }
 
        public interface SpaceCharFilter
        {
            public boolean isSpaceChar(int ch);
        }
    }
   public static long modularExponentiation(long x,long n,long M)
   {
       long result=1;
       while(n>0)
       {
           if(n % 2 ==1)
               result=(result%M * x%M)%M;
           x=(x%M * x%M)%M;
           n=n/2;
       }
       return result;
   }
    static class pair implements Comparable<pair>{
        Integer x;
        Long y;
        Integer z;
        pair(Integer x,long  w,int z){
            this.x=x;
            this.y=w;
            this.z=z;
        }
         public int compareTo(pair o) {
                int result = x.compareTo(o.x);
                if(result==0)
                    result = y.compareTo(o.y);
                
            return result;
            }  
         public String toString(){
            return (x+" "+y);
        }
  }
    
}
