#pragma GCC optimize("O3")
#pragma GCC target("avx2")
#include <bits/stdc++.h>
using namespace std;
#define f first
#define s second
#ifdef LOCAL
#define err cerr
#else
#define err if (0) cerr
#endif
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<vector<int>> grid;
if (n < m) {
grid.resize(n, vector<int>(m));
for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) {
char c;
cin >> c;
grid[i][j] = c == '0';
}
} else {
grid.resize(m, vector<int>(n));
for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) {
char c;
cin >> c;
grid[j][i] = c == '0';
}
swap(n, m);
}
vector<vector<int>> psum(n+1, vector<int>(m+1, 0));
for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) psum[i+1][j+1] = grid[i][j];
for (int i = 0; i < n; i++) for (int j = 0; j <= m; j++) psum[i+1][j] += psum[i][j];
for (int i = 0; i <= n; i++) for (int j = 0; j < m; j++) psum[i][j+1] += psum[i][j];
int mx = n, my = m;
for (int i = 0; i < n; i++) {
vector<pair<int, int>> ran;
for (int j = 0; j < m; j++) {
if (grid[i][j]) continue;
if (!ran.size() || ran.back().s != j)
ran.push_back({j, j+1});
else
ran.back().s++;
}
for (auto j: ran) my = min(my, j.s-j.f);
}
for (int i = 0; i < m; i++) {
vector<pair<int, int>> ran;
for (int j = 0; j < n; j++) {
if (grid[j][i]) continue;
if (!ran.size() || ran.back().s != j)
ran.push_back({j, j+1});
else
ran.back().s++;
}
for (auto j: ran) mx = min(mx, j.s-j.f);
}
int upt = 32-__builtin_clz(my);
// proof by ac doesn't work :(
if (1) {
int ans = 0;
for (int x = 1; x <= mx; x++) {
int y = 0;
for (int l = upt; l--;) {
int k = y+(1<<l);
vector<vector<int>> psa(n+1, vector<int>(m+1, 0));
for (int i = 0; i <= n-x; i++) {
for (int j = 0; j <= m-k; j++) {
if (psum[i+x][j+k]-psum[i+x][j]-psum[i][j+k]+psum[i][j] == 0) {
psa[i+x][j+k]++;
psa[i+x][j]--;
psa[i][j+k]--;
psa[i][j]++;
}
}
}
for (int i = 0; i < n; i++) for (int j = 0; j <= m; j++) psa[i+1][j] += psa[i][j];
for (int i = 0; i <= n; i++) for (int j = 0; j < m; j++) psa[i][j+1] += psa[i][j];
bool good = true;
for (int i = 0; i < n && good; i++) for (int j = 0; j < m && good; j++) good = (!psa[i][j]) == grid[i][j];
if (good) y += 1<<l;
}
ans = max(ans, x*y);
err << x << " " << y << "\n";
}
cout << ans << "\n";
return 0;
}
cout << mx*my << "\n";
}
