#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int N = 453;
int L[N][N], R[N][N], U[N][N], D[N][N], J[N], a[N][N], T[N];
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++)
U[i][j] = (a[i][j] ? U[i - 1][j] + 1 : 0);
for (int i = n; i >= 1; --i)
D[i][j] = (a[i][j] ? D[i + 1][j] + 1 : 0);
for (int i = 1; i <= n; i++) if (a[i][j])
X = min(X, U[i][j] + D[i][j] - 1);
}
fill(J + 1, J + X + 1, 1e9);
for (int j = 1; j <= m; j++)
for (int i = 1; i <= n; i++)
if (a[i][j] && !a[i - 1][j]) {
int pref_L = 1e9, pref_R = 1e9;
for (int k = i; k < i + D[i][j]; k++) {
pref_L = min(pref_L, L[k][j]);
pref_R = min(pref_R, R[k][j]);
J[1] = min(J[1], L[k][j] + R[k][j] - 1);
J[U[k][j]] = min(J[U[k][j]], pref_L + pref_R - 1);
}
pref_L = 1e9, pref_R = 1e9;
for (int k = i + D[i][j] - 1; k >= i; --k) {
pref_L = min(pref_L, L[k][j]);
pref_R = min(pref_R, R[k][j]);
J[D[k][j]] = min(J[D[k][j]], pref_L + pref_R - 1);
}
}
for (int h = 2; h <= X; h++) J[h] = min(J[h], J[h - 1]);
int ans = 0;
for (int h = 1; h <= X; h++) ans = max(ans, h * J[h]);
cout << ans << "\n";
}
