#include <iostream>
using namespace std;
const int N = 2505;
int a[N][N], ans[N];
int L[N][N], R[N][N];
int main() {
int n, m;
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');
}
}
for (int i = 1 ; i <= n ; ++ i) {
ans[i] = m;
}
int lim = n;
for (int rep = 0 ; rep < 2 ; ++ rep) {
for (int i = 1 ; i <= n ; ++ i) {
for (int j = 1 ; j <= m ; ++ j) {
if (a[i][j]) L[i][j] = L[i][j - 1] + 1;
else L[i][j] = 0;
}
for (int j = m ; j >= 1 ; -- j) {
if (a[i][j]) R[i][j] = R[i][j + 1] + 1;
else R[i][j] = 0;
}
for (int j = 1 ; j <= m ; ++ j) {
if (a[i][j]) ans[1] = min(ans[1], L[i][j] + R[i][j] - 1);
}
}
for (int j = 1 ; j <= m ; ++ j) {
int cnt = 0;
int LX = -1, RX = -1;
for (int i = 1 ; i <= n + 1 ; ++ i) {
if (a[i][j]) {
cnt++;
if (cnt == 1) {
LX = L[i][j], RX = R[i][j];
}
LX = min(LX, L[i][j]), RX = min(RX, R[i][j]);
ans[cnt] = min(ans[cnt], LX + RX - 1);
} else {
if (cnt > 0) lim = min(lim, cnt);
LX = RX = -1;
cnt = 0;
}
}
}
for (int i = 1 ; i <= n / 2 ; ++ i) {
for (int j = 1 ; j <= m ; ++ j) {
swap(a[i][j], a[n - i + 1][j]);
}
}
}
int res = 0;
for (int i = 1 ; i <= lim ; ++ i) {
//cerr << i << " " << ans[i] << endl;
ans[i + 1] = min(ans[i + 1], ans[i]);
res = max(res, ans[i] * i);
}
cout << res;
}
