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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.io.IOException;
import java.util.InputMismatchException;
import java.io.InputStreamReader;
import java.io.BufferedOutputStream;
import java.util.StringTokenizer;
import java.io.Closeable;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.Flushable;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
	static class TaskAdapter implements Runnable {
		@Override
		public void run() {
			InputStream inputStream = System.in;
			OutputStream outputStream = System.out;
			Input in = new Input(inputStream);
			Output out = new Output(outputStream);
			BMaximumSubmatrix2 solver = new BMaximumSubmatrix2();
			solver.solve(1, in, out);
			out.close();
		}
	}

	public static void main(String[] args) throws Exception {
		Thread thread = new Thread(null, new TaskAdapter(), "", 1<<29);
		thread.start();
		thread.join();
	}
	static class BMaximumSubmatrix2 {
		int n;
		int m;
		int[][] cnt;
		int[][] memo;
		int[][] d;
		int[] ends;
		int[] sum;

		public BMaximumSubmatrix2() {
		}

		public int dp(int x, int y) {
			if(memo[x][y]!=-1) {
				return memo[x][y];
			}else if(x==y) {
				return memo[x][y] = sum[x];
			}
			return memo[x][y] = dp(x, y-1)-d(x, y-1);
		}

		public int d(int x, int y) {
			if(d[x][y]!=-1) {
				return d[x][y];
			}else if(x==y) {
				return ends[y];
			}
			return d[x][y] = d(x+1, y)-cnt[x+1][y];
		}

		public void solve(int kase, Input in, Output pw) {
			n = in.nextInt();
			m = in.nextInt();
			cnt = new int[m][m];
			sum = new int[m+1];
			ends = new int[m];
			for(int i = 0; i<n; i++) {
				String s = in.next();
				for(int j = 0; j<m; ) {
					for(; j<m&&s.charAt(j)=='0'; j++) ;
					if(j!=m) {
						int start = j;
						for(; j<m&&s.charAt(j)=='1'; j++) ;
						cnt[start][j-1]++;
						ends[j-1]++;
						sum[start]++;
						sum[j]--;
					}
				}
			}
			for(int i = 1; i<m; i++) {
				sum[i] += sum[i-1];
			}
			memo = new int[m][m];
			d = new int[m][m];
			for(int i = 0; i<m; i++) {
				Arrays.fill(memo[i], -1);
				Arrays.fill(d[i], -1);
			}
			int ans = 0;
			for(int i = 0; i<m; i++) {
				for(int j = i; j<m; j++) {
					ans = Math.max(ans, (j-i+1)*dp(i, j));
				}
			}
			pw.println(ans);
		}

	}

	static class Input {
		BufferedReader br;
		StringTokenizer st;

		public Input(InputStream is) {
			this(is, 1<<20);
		}

		public Input(InputStream is, int bs) {
			br = new BufferedReader(new InputStreamReader(is), bs);
			st = null;
		}

		public boolean hasNext() {
			try {
				while(st==null||!st.hasMoreTokens()) {
					String s = br.readLine();
					if(s==null) {
						return false;
					}
					st = new StringTokenizer(s);
				}
				return true;
			}catch(Exception e) {
				return false;
			}
		}

		public String next() {
			if(!hasNext()) {
				throw new InputMismatchException();
			}
			return st.nextToken();
		}

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

	}

	static class Output implements Closeable, Flushable {
		public StringBuilder sb;
		public OutputStream os;
		public int BUFFER_SIZE;
		public boolean autoFlush;
		public String LineSeparator;

		public Output(OutputStream os) {
			this(os, 1<<16);
		}

		public Output(OutputStream os, int bs) {
			BUFFER_SIZE = bs;
			sb = new StringBuilder(BUFFER_SIZE);
			this.os = new BufferedOutputStream(os, 1<<17);
			autoFlush = false;
			LineSeparator = System.lineSeparator();
		}

		public void println(int i) {
			println(String.valueOf(i));
		}

		public void println(String s) {
			sb.append(s);
			println();
			if(autoFlush) {
				flush();
			}else if(sb.length()>BUFFER_SIZE >> 1) {
				flushToBuffer();
			}
		}

		public void println() {
			sb.append(LineSeparator);
		}

		private void flushToBuffer() {
			try {
				os.write(sb.toString().getBytes());
			}catch(IOException e) {
				e.printStackTrace();
			}
			sb = new StringBuilder(BUFFER_SIZE);
		}

		public void flush() {
			try {
				flushToBuffer();
				os.flush();
			}catch(IOException e) {
				e.printStackTrace();
			}
		}

		public void close() {
			flush();
			try {
				os.close();
			}catch(IOException e) {
				e.printStackTrace();
			}
		}

	}
}


