#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n, m;
cin >> n >> m;
string s[n + 5];
int lr = m;
for (int i = 0; i < n; i++) {
cin >> s[i];
int cnt = -1;
for (int j = 0; j < m; j++) {
if (s[i][j] == '1') {
if (cnt == -1) cnt = 1;
else cnt++;
} else {
if (cnt == -1) continue;
lr = min(lr, cnt);
cnt = -1;
}
}
if (cnt != -1) {
lr = min(lr, cnt);
cnt = -1;
}
}
int ud = n;
for (int j = 0; j < m; j++) {
int cnt = -1;
for (int i = 0; i < n; i++) {
//cerr << "ud: " << ud << endl;
if (s[i][j] == '1') {
if (cnt == -1) cnt = 1;
else cnt++;
} else {
if (cnt == -1) continue;
ud = min(ud, cnt);
cnt = -1;
}
}
if (cnt != -1) {
ud = min(ud, cnt);
cnt = -1;
}
}
//cerr << "ud: " << ud << " lr: " << lr << endl;
cout << ud*lr << '\n';
return 0;
}
