#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string.h>
using namespace std;
#define endl '\n'
#define pi pair<int, int>
const int maxn = 2502;
int n, m;
int a[maxn][maxn];
bool solve(int x, int y){
int b[maxn][maxn];
memset(b, 0, sizeof(b));
for(int i = x; i <= n; i++){
for(int j = y; j <= m; j++){
if(a[i][j] - a[i - x][j] - a[i][j - y] + a[i - x][j - y] == x * y){
b[i - x + 1][j - y + 1]++;
b[i - x + 1][j + 1]--;
b[i + 1][j - y + 1]--;
b[i + 1][j + 1]++;
}
}
}
int amt = a[n][m];
for(int i = 1; i <= n; i++){
for(int j = 1; j <= m; j++){
b[i][j] += b[i - 1][j] + b[i][j - 1] - b[i - 1][j - 1];
amt -= (b[i][j] > 0);
}
}
return amt == 0;
}
int solveh(int x){
int l = 0, r = n + 1;
while(r - l > 1){
int mid = (l + r) / 2;
if(solve(x, mid)) l = mid;
else r = mid;
}
return l;
}
int solvew(int x){
int l = 0, r = n + 1;
while(r - l > 1){
int mid = (l + r) / 2;
if(solve(mid, x)) l = mid;
else r = mid;
}
return l;
}
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 - '0' + a[i - 1][j] + a[i][j - 1] - a[i - 1][j - 1];
}
}
int ret = max(solveh(1) * solvew(solveh(1)), solvew(1) * solveh(solvew(1)));
cout << ret << endl;
return 0;
}
