#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int N = 2512;
int s[N][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;
s[i][j] = c - '0';
}
int inf = 1e9;
int best_width = inf, best_height = inf;
for (int i = 1; i <= n; i++) {
vector<pair<int, int>> b;
b.reserve(m + 1);
b.emplace_back(s[i][1], 1);
for (int j = 2; j <= m; j++) if (s[i][j] == s[i][j - 1]) b.back().second += 1;
else b.emplace_back(s[i][j], 1);
for (auto [x, y] : b) if (x)
best_width = min(best_width, y);
}
for (int j = 1; j <= m; j++) {
vector<pair<int, int>> b;
b.reserve(n + 1);
b.emplace_back(s[1][j], 1);
for (int i = 2; i <= n; i++) if (s[i][j] == s[i - 1][j]) b.back().second += 1;
else b.emplace_back(s[i][j], 1);
for (auto [x, y] : b) if (x)
best_height = min(best_height, y);
}
assert(best_width < inf && best_height < inf);
cout << best_width * best_height << "\n";
}
