#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
typedef long long ll;
const ll MAXN = 25e2 + 5;
const ll INF = 1e9;
#define endl '\n'
#define pll pair <ll, ll>
#define fi first
#define se second
ll n, m;
string a [MAXN];
ll pf [MAXN][MAXN];
bool uda [MAXN][MAXN];
int main(){
cin >> n >> m;
for(ll i = 1; i <= n; i++){
string dum; cin >> dum;
a[i] = '2' + dum;
}
if(n == 1 && m == 1){
cout << a[1][1] << endl;
exit(0);
}
for(ll i = 1; i <= n; i++){
for(ll j = 1; j <= m; j++){
pf[i][j] = pf[i][j-1];
if(a[i][j] == '1') pf[i][j]++;
}
}
for(ll j = 1; j <= m; j++){
for(ll i = 1; i <= n; i++){
pf[i][j] += pf[i-1][j];
}
}
// cout << endl;
// for(ll i = 1; i <= n; i++){
// for(ll j = 1; j <= m; j++){
// cout << pf[i][j] << " ";
// }
// cout << endl;
// }
// cout << endl;
ll mx = 0;
for(ll x = 1; x <= n; x++){
for(ll y = 1; y <= m; y++){
for(ll i = 1; i <= n; i++){
for(ll j = 1; j <= m; j++) uda[i][j] = false;
}
for(ll i = 1; i+x-1 <= n; i++){
for(ll j = 1; j+y-1 <= m; j++){
ll sum = pf[i+x-1][j+y-1] - pf[i-1][j+y-1] - pf[i+x-1][j-1] + pf[i-1][j-1];
if(sum == x*y){
for(ll lx = i; lx <= i+x-1; lx++){
for(ll ly = j; ly <= j+y-1; ly++){
uda[lx][ly] = true;
}
}
}
}
}
bool bnr = true;
for(ll i = 1; i <= n; i++){
for(ll j = 1; j <= m; j++){
if(!uda[i][j] && a[i][j] == '1'){
bnr = false;
break;
}
}
}
if(bnr){
mx = max(mx, x*y);
}
}
}
cout << mx << endl;
}
