#include <bits/stdc++.h>
//#pragma GCC optimize("unroll-loops")
//#pragma GCC optimize("-O3")
//#pragma GCC optimize("Ofast")
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define sz(x) ((int)x.size())
#define MP make_pair
#define ft first
#define sd second
#define pii pair<int, int>
#define PB push_back
using namespace std;
using namespace __gnu_pbds;
template <class T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int N = 2510;
const int oo = 2e9;
int n, m, ans, a[N][N], mx = oo, pr[N][N], best[N], nt[N][N];
int main(){
ios_base::sync_with_stdio(0); cin.tie(0);
// freopen("in.txt","r",stdin);
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' ? 1 : 0);
}
for (int j = 1; j <= m; j++){
for (int i = 1; i <= n; ){
if (a[i][j] == 0)
i++;
else {
int i1 = i;
while (i1 <= n && a[i1][j] == 1)
i1++;
mx = min(mx, i1 - i);
i = i1;
}
}
}
if (mx == oo){
cout << n * m;
return 0;
}
fill(best, best + n + 1, oo);
for (int i = 1; i <= n; i++){
int pre = 0;
for (int j = 1; j <= m; j++){
if (a[i][j] == 0)
pre = j;
pr[i][j] = pre + 1;
}
pre = m + 1;
for (int j = m; j > 0; j--){
if (a[i][j] == 0)
pre = j;
nt[i][j] = pre - 1;
}
}
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++) {
int mn = oo, mn1 = oo;
int MN = oo, MN1 = oo;
bool bd1 = 0, bd2 = 0;
// if (i == 5 && j == 5){
// cerr << "OK\n";
// }
for (int h = 1; h <= mx; h++){
int ii = i - h + 1;
int i2 = i + h - 1;
if (i < h) bd1 = 1;
if (i + h - 1 > n) bd2 = 1;
if (!bd1 && a[ii][j] == 0) bd1 = 1;
if (!bd2 && a[i2][j] == 0) bd2 = 1;
if (bd1 && bd2) break;
int res = 0;
if (!bd1){
mn = min(mn, j - pr[ii][j] + 1);
mn1 = min(mn1, nt[ii][j] - j);
res = max(res, mn + mn1);
}
if (!bd2){
MN = min(MN, j - pr[i2][j] + 1);
MN1 = min(MN1, nt[i2][j] - j);
res = max(res, MN + MN1);
}
best[h] = min(best[h], res);
}
}
for (int i = 1; i <= mx; i++) {
if (best[i] == oo) return -1;
ans = max(ans, best[i] * i);
}
cout << ans << '\n';
return 0;
}
