#include <bits/stdc++.h>
using namespace std;
#define int long long
#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 == '1';
}
} 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 == '1';
}
swap(n, m);
}
// lets try proof by ac!
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);
}
cout << mx*my << "\n";
}
