include iostream include string include vector include iomanip include

#include <iostream>
#include <string>
#include <vector>
#include <iomanip>
#include <cmath>
#include <set>
#include <queue>
#include <cstdio>
#include <algorithm>
#include <map>

using namespace std;

const int N = 1000;
string rows[N];
int maxUp[N][N];
int smallerToLeft[N];
int smallerToRight[N];

int main() {
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	int n, m;
	cin >> n >> m;
	for (int i = 0; i < n; ++i)
		cin >> rows[i];

	for (int j = 0; j < m; ++j)
		maxUp[0][j] = rows[0][j] - '0';

	for (int i = 1; i < n; ++i)
		for (int j = 0; j < m; ++j){
			if (rows[i][j] == '0') maxUp[i][j] = 0;
			else maxUp[i][j] = 1 + maxUp[i - 1][j];
		}

	int ans = 0;
	for (int i = 0; i < n; ++i){
		int* h = maxUp[i];
		for (int j = 0; j < m; ++j){
			smallerToLeft[j] = j - 1;
			while (smallerToLeft[j] >= 0 && h[smallerToLeft[j]] >= h[j])
				smallerToLeft[j] = smallerToLeft[smallerToLeft[j]];
		}
		for (int j = m - 1; j >= 0; --j)
		{
			smallerToRight[j] = j + 1;
			while (smallerToRight[j] < m && h[smallerToRight[j]] >= h[j])
				smallerToRight[j] = smallerToRight[smallerToRight[j]];
		}
		for (int j = 0; j < m; ++j)
		{
			int lb = smallerToLeft[j] + 1;
			int rb = smallerToRight[j] - 1;
			ans = max(ans, (rb - lb + 1) * h[j]);
		}
	}
	cout << ans << endl;	
	return 0;
}