#include <bits/stdc++.h>
using namespace std;
int n, m, ps[2501][2501];
bool grid[2501][2501];
int main() {
cin >> n >> m;
for (int r = 0; r < n; ++r) {
for (int c = 0; c < m; ++c) {
char x;
cin >> x;
grid[r][c] = x == '1';
ps[r + 1][c + 1] = ps[r][c + 1] + ps[r + 1][c] - ps[r][c] + grid[r][c];
}
}
// cerr << n << ' ' << m << endl;
// for (int r = 0; r < n; ++r) {
// for (int c = 0; c < m; ++c) {
// cerr << grid[r][c];
// }
// cerr << endl;
// }
auto can = [&] (int R, int C) {
if (not (R * C)) return true;
for (int r = n; r--;) {
for (int c = m; c--;) {
if (not grid[r][c]) continue;
// cerr << r << ' ' << c << endl;
if (not grid[r + 1][c] and not grid[r][c + 1]) {
if (r < R - 1 or c < C - 1) return false;
if (ps[r + 1][c + 1] - ps[r - R + 1][c + 1] - ps[r + 1][c - C + 1] + ps[r - R + 1][c - C + 1] < R * C) {
return false;
}
} else if (not grid[r + 1][c]) {
if (r < R - 1) return false;
if (ps[r + 1][c + 1] - ps[r + 1][c] - ps[r - R + 1][c + 1] + ps[r - R + 1][c] < R) {
return false;
}
} else if (not grid[r][c + 1]) {
if (c < C - 1) return false;
if (ps[r + 1][c + 1] - ps[r][c + 1] - ps[r + 1][c - C + 1] + ps[r][c - C + 1] < C) {
return false;
}
}
}
}
return true;
};
// cerr << can(3, 1);
int ans = 0;
for (int R = 1, C = m; R <= n; ++R) {
while (not can(R, C)) --C;
ans = max(ans, R * C);
}
cout << ans;
}
