#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
ios::sync_with_stdio(false); cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<string> a(n);
for (auto &i : a)
cin >> i;
if ((ll)n * m * n * m * n * m > (int)1e8) {
int mn1 = n, mn2 = m;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (a[i][j] == '0') continue;
int l = i, r = i;
while (0 < l && a[l - 1][j] == '1') l--;
while (r + 1 < n && a[r + 1][j] == '1') r++;
mn1 = min(mn1, r - l + 1);
l = r = j;
while (0 < l && a[i][l - 1] == '1') l--;
while (r + 1 < m && a[i][r + 1] == '1') r++;
mn2 = min(mn2, r - l + 1);
}
}
return cout << mn1 * mn2, 0;
}
int mx = 1;
for (int x = 1; x <= n; x++) {
for (int y = 1; y <= m; y++) {
if (x * y <= mx) continue;
bool ok = true;
vector<vector<bool>> vis(n, vector<bool>(m));
for (int i = 0; i + x <= n; i++) {
for (int j = 0; j + y <= m; j++) {
if (a[i][j] == '0') continue;
bool tr = true;
for (int k = i; k < i + x && tr; k++) {
for (int l = j; l < j + y && tr; l++)
tr = (a[k][l] == '1');
}
ok = vis[i][j];
if (!tr) continue;
for (int k = i; k < i + x; k++) {
for (int l = j; l < j + y; l++)
vis[k][l] = true;
}
ok = vis[i][j];
}
}
for (int i = 0; i < n && ok; i++) {
for (int j = 0; j < m && ok; j++)
ok = (a[i][j] == '0' || vis[i][j]);
}
if (ok) mx = max(mx, x * y);
}
}
cout << mx;
}
