#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int N = 453;
int L[N][N], R[N][N], D[N][N][N], J[N], a[N][N], T[N], p;
int Q[N], l, r;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n, m;
cin >> n >> m;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++) {
char c;
cin >> c;
a[i][j] = c - '0';
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++)
L[i][j] = (a[i][j] ? L[i][j - 1] + 1 : 0);
for (int j = m; j >= 1; --j)
R[i][j] = (a[i][j] ? R[i][j + 1] + 1 : 0);
}
int X = 1e9;
for (int j = 1; j <= m; j++) {
for (int i = 1; i <= n; i++) T[i] = (a[i][j] ? T[i - 1] + 1 : 0);
for (int i = 1; i <= n; i++)
if (T[i] > 0 && T[i + 1] == 0) X = min(X, T[i]);
}
for (int h = 1; h <= X; h++) {
J[h] = 1e9;
for (int j = 1; j <= m; j++) { // fix a column j
p = 0;
for (int i = 1; i <= n + 1; i++) {
if (a[i][j]) {
T[p++] = L[i][j] + R[i][j] - 1;
continue;
}
if (p == 0) continue;
assert(h <= p);
l = 0, r = -1;
for (int k = 0; k < p; k++) {
while (r >= 0 && T[k] <= T[Q[r]]) --r;
Q[++r] = k;
if (k >= h - 1) J[h] = min(J[h], T[Q[l]]);
if (k >= h)
while (l <= r && Q[l] >= k - h) l++;
}
p = 0;
}
}
}
int ans = 0;
for (int h = 1; h <= n; h++) ans = max(ans, h * J[h]);
cout << ans << "\n";
}
