#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
/*
0011
0011
1110
1100
*/
void solve (int X) {
int n, m; cin >> n >> m;
vector <vector <char>> a(n + 1, vector <char> (m + 1));
vector <vector <int>> up(n + 1, vector <int> (m + 1, 0));
vector <vector <int>> down(n + 2, vector <int> (m + 1, 0));
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> a[i][j];
}
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
up[i][j] = (a[i][j] == '0' ? 0 : 1 + up[i - 1][j]);
}
}
for (int i = n; i >= 1; i--) {
for (int j = 1; j <= m; j++) {
down[i][j] = (a[i][j] == '0' ? 0 : 1 + down[i + 1][j]);
}
}
int dx = n, dy = m;
for (int i = 1; i <= n; i++) {
int cnt = 0;
for (int j = 1; j <= m; j++) {
if (a[i][j] == '1') {
cnt++;
} else if (cnt > 0) {
dy = min(dy, cnt);
cnt = 0;
}
}
if (cnt > 0) {
dy = min(dy, cnt);
cnt = 0;
}
}
for (int j = 1; j <= m; j++) {
int cnt = 0;
for (int i = 1; i <= n; i++) {
if (a[i][j] == '1') {
cnt++;
} else if (cnt > 0) {
dx = min(dx, cnt);
cnt = 0;
}
}
if (cnt > 0) {
dx = min(dx, cnt);
cnt = 0;
}
}
vector <int> ee(dx + 1, dy);
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
if (a[i][j] == '0') {
continue;
}
int cur = dx;
for (int k = j; k >= 1; k--) {
if (a[i][k] == '0') {
break;
}
cur = min(cur, down[i][k] + up[i][k] - 1);
int p = j;
while (p + 1 <= m && down[i][p + 1] + up[i][p + 1] - 1 >= cur) {
p++;
}
while (k - 1 >= 1 && down[i][k - 1] + up[i][k - 1] - 1 >= cur) {
k--;
}
ee[cur] = min(ee[cur], p - k + 1);
//cout << i << " " << j << " " << p << " " << k << ": " << cur << " " << p - k + 1 << '\n';
}
}
}
int mx = 0;
for (int i = 1; i <= dx; i++) {
//cout << i << ": " << ee[i] << '\n';
mx = max(mx, i * ee[i]);
}
cout << mx << '\n';
}
signed main () {
#ifndef ONLINE_JUDGE
//freopen("input_file", "r", stdin);
//freopen("output_file", "w", stdout);
#endif
ios::sync_with_stdio(0); cin.tie(0);
int tc = 1; //cin >> tc;
for (int i = 1; i <= tc; i++) solve(i);
}
