#include "bits/stdc++.h"
// @JASPER'S BOILERPLATE
using namespace std;
using ll = long long;
#ifdef JASPER
#include "debug.h"
#else
#define debug(...) 166
#endif
signed main() {
cin.tie(0) -> sync_with_stdio(0);
int n, m;
cin >> n >> m;
vector <vector <int>> a(n + 5, vector <int> (m + 5, 0));
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= m; ++j) {
char x; cin >> x;
a[i][j] = x - '0';
}
}
// for (int i = 1; i <= n; ++i)
// for (int j = 1; j <= m; ++j)
// cout << a[i][j] << " \n"[j == m];
//sub1: shortest consecutive 1ss
if (n == 1 || m == 1) {
if (n == 1) {
int ans = 1e9;
for (int i = 1; i <= m; ++i) {
if (a[1][i] == 0) continue;
int cur = 0;
while (i <= m && a[1][i]) {
++cur;
++i;
}
ans = min(ans, cur);
}
cout << ans << "\n";
return 0;
}
if (m == 1) {
int ans = 1e9;
for (int i = 1; i <= n; ++i) {
if (a[i][1] == 0) continue;
int cur = 0;
while (i <= n && a[i][1]) {
++cur;
++i;
}
ans = min(ans, cur);
}
cout << ans << "\n";
return 0;
}
}
// sub3
if (n <= 450 && m <= 450) {
vector <vector <int>> prf(n + 5, vector <int> (m + 5, 0));
int earth = 0;
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= m; ++j) {
earth += (a[i][j] == 0);
prf[i][j] = prf[i][j - 1] + prf[i - 1][j] - prf[i - 1][j - 1] + a[i][j];
}
}
int ans = 0;
for (int x = 1; x <= n; ++x) {
for (int y = 1; y <= m; ++y) {
if (x * y <= ans) continue;
// prf(l)++, prf(r + 1)--;
vector <vector <int>> dmg(n + 2, vector <int> (m + 2, 0));
for (int i = 1; i + x - 1 <= n; ++i) {
for (int j = 1; j + y - 1 <= m; ++j) {
int I = i + x - 1, J = j + y - 1;
if (prf[I][J] + prf[i - 1][j - 1] - prf[I][j - 1] - prf[i - 1][J] == x * y) {
dmg[i][j] += 1;
dmg[I + 1][j] -= 1;
dmg[i][J + 1] -= 1;
dmg[I + 1][J + 1] += 1;
}
}
}
// if (x == 3 && y == 1) {
// cout << "\n";
// for (int i = 1; i <= n; ++i)
// for (int j = 1; j <= m; ++j)
// cout << dmg[i][j] << " \n"[j == m];
// }
for (int i = 1; i <= n; ++i)
for (int j = 1; j <= m; ++j)
dmg[i][j] += dmg[i - 1][j] + dmg[i][j - 1] - dmg[i - 1][j - 1];
// if (x == 3 && y == 1) {
// cout << "\n";
// for (int i = 1; i <= n; ++i)
// for (int j = 1; j <= m; ++j)
// cout << dmg[i][j] << " \n"[j == m];
// }
bool valid = 1;
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= m; ++j) {
if (a[i][j] && !dmg[i][j])
valid = 0;
}
}
if (valid) ans = max(ans, x * y);
}
}
cout << ans << "\n";
}
}
