#include <iostream>
#include <cstdio>
#include <algorithm>
#include <stack>
using namespace std;
#define endl '\n'
#define ll long long
#define pi pair<int, int>
#define f first
#define s second
const int maxn = 2502;
int n, m;
int a[maxn][maxn], h[maxn][maxn], v[maxn][maxn];
stack<int> stk;
int main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> m;
for(int i = 1; i <= n; i++)
for(int j = 1; j <= m; j++){
char c;
cin >> c;
a[i][j] = c == '1';
h[i][j] = a[i][j] + h[i][j - 1];
v[i][j] = a[i][j] + v[i - 1][j];
}
int x = n, y = m;
for(int i = 1; i <= n; i++){
for(int j = 1; j <= m + 1; j++){
a[i][j] = a[i][j] * (a[i - 1][j] + 1);
while(!stk.empty() && a[i][j] <= a[i][stk.top()]){
int c = stk.top();
stk.pop();
int dx = a[i][c], dy = j - (stk.empty() ? 0 : stk.top()) - 1;
if(h[i + 1][j - 1] - h[i + 1][j - dy - 1] != dy && v[i][j] - v[i - dx][j] != dx){
x = min(x, dx), y = min(y, dy);
}
}
stk.push(j);
}
while(!stk.empty()) stk.pop();
}
cout << (x * y) << endl;
return 0;
}
