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.math.*;
import java.util.*;

import static java.util.Arrays.fill;
import static java.lang.Math.*;
import static java.util.Arrays.sort;
import static java.util.Collections.sort;


public class B375 
{

	public static int mod = 1000000007;
	public static long INF = (1L << 60);
	static FastScanner2 in = new FastScanner2();
	static OutputWriter out = new OutputWriter(System.out);
	
	
	
	public static void main(String[] args) 
	{

		int n=in.nextInt();
		int m=in.nextInt();
		int[][] arr=new int[n+1][m+1];
		for(int i=1;i<=n;i++)
		{
			String s=in.nextLine();
			for(int j=1;j<=m;j++)
			{
				arr[i][j]=s.charAt(j-1)-'0';
			}
		}
		
		int[][] right=new int[m+1][n+1];
		for(int i=1;i<=n;i++)
		{
			for(int j=m;j>=1;j--)
			{
				if(arr[i][j]==1)
				{
					if(j+1<=m)
						right[j][i]=right[j+1][i]+1;
					else
						right[j][i]=1;
				}
				else
					right[j][i]=0;
				//out.print(right[j][i]+" ");
			}
			//out.println();
		}
		for(int i=1;i<=m;i++)
		{
			Arrays.sort(right[i]);
		}
		int answer=0;
		for(int i=1;i<=m;i++)
		{
			for(int j=1;j<=n;j++)
			{
				answer=max(answer, right[i][j]*(n-j+1));
			}
		}
		out.println(answer);
		out.close();

	}
	
	public static long pow(long x, long n) 
	{
		long res = 1;
		for (long p = x; n > 0; n >>= 1, p = (p * p)) 
		{
			if ((n & 1) != 0) 
			{
				res = (res * p);
			}
		}
		return res;
	}
	
	public static long pow(long x, long n, long mod) 
	{
		long res = 1;
		for (long p = x; n > 0; n >>= 1, p = (p * p) % mod) 
		{
			if ((n & 1) != 0) 
			{
				res = (res * p % mod);
			}
		}
		return res;
	}

	public static long gcd(long n1, long n2)
	{
		long r;
		while (n2 != 0) 
		{
			r = n1 % n2;
			n1 = n2;
			n2 = r;
		}
		return n1;
	}

	public static long lcm(long n1, long n2) 
	{
		long answer = (n1 * n2) / (gcd(n1, n2));
		return answer;
	}
	
	static class FastScanner2 
	{
		private byte[] buf = new byte[1024];
		private int curChar;
		private int snumChars;

		public int read() 
		{
			if (snumChars == -1)
				throw new InputMismatchException();
			if (curChar >= snumChars) 
			{
				curChar = 0;
				try 
				{
					snumChars = System.in.read(buf);
				} catch (IOException e) 
				{
					throw new InputMismatchException();
				}
				if (snumChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}

		public String nextLine() 
		{
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do 
			{
				res.appendCodePoint(c);
				c = read();
			} 
			while (!isEndOfLine(c));
			return res.toString();
		}

		public String nextString() 
		{
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do 
			{
				res.appendCodePoint(c);
				c = read();
			} 
			while (!isSpaceChar(c));
			return res.toString();
		}

		public long nextLong()
		{
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			long res = 0;
			do 
			{
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} 
			while (!isSpaceChar(c));
			return res * sgn;
		}

		public int nextInt() 
		{
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			int res = 0;
			do 
			{
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} 
			while (!isSpaceChar(c));
			return res * sgn;
		}

		public int[] nextIntArray(int n)
		{
			int[] arr = new int[n];
			for (int i = 0; i < n; i++) 
			{
				arr[i] = nextInt();
			}
			return arr;
		}

		public long[] nextLongArray(int n)
		{
			long[] arr = new long[n];
			for (int i = 0; i < n; i++) 
			{
				arr[i] = nextLong();
			}
			return arr;
		}

		private boolean isSpaceChar(int c)
		{
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		private boolean isEndOfLine(int c) 
		{
			return c == '\n' || c == '\r' || c == -1;
		}
	}

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

		public InputReader(InputStream inputstream) 
		{
			reader = new BufferedReader(new InputStreamReader(inputstream));
			tokenizer = null;
		}

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

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

		public int[] nextIntArray(int n) 
		{
			int a[] = new int[n];
			for (int i = 0; i < n; i++) 
			{
				a[i] = nextInt();
			}
			return a;
		}

		public long[] nextLongArray(int n)
		{
			long a[] = new long[n];
			for (int i = 0; i < n; i++) 
			{
				a[i] = nextLong();
			}
			return a;
		}

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

	static class OutputWriter 
	{
		private final PrintWriter writer;

		public OutputWriter(OutputStream outputStream) 
		{
			writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
		}

		public OutputWriter(Writer writer)
		{
			this.writer = new PrintWriter(writer);
		}

		public void print(Object... objects)
		{
			for (int i = 0; i < objects.length; i++) 
			{
				if (i != 0)
					writer.print(' ');
				writer.print(objects[i]);
			}
		}

		public void println(Object... objects)
		{
			print(objects);
			writer.println();
		}

		public void close() 
		{
			writer.close();
		}

		public void flush() 
		{
			writer.flush();
		}
	}
private static boolean oj = System.getProperty("ONLINE_JUDGE") != null;
	
	private static void debug(Object... o) 
	{
		if (!oj)
			System.out.println(Arrays.deepToString(o));
	}
	private static void tr(Object... o) 
	{
		if (!oj)
			System.out.println(Arrays.deepToString(o));
	}
}