#include "bits/stdc++.h"
using namespace std;
using ll = long long;
const int inf = 1e9, N = 1e6 + 5;
int main() {
cin.tie(0)->sync_with_stdio(false);
#ifdef sunnatov
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#else
// freopen("game.in", "r", stdin);
// freopen("game.out", "w", stdout);
#endif
int n, m;
cin >> n >> m;
vector<vector<char>> a(n + 1, vector<char>(m + 1));
vector<vector<int>> pref(n + 1, vector<int>(m + 1));
for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++) {
cin >> a[i][j];
pref[i][j] = pref[i][j - 1] + pref[i - 1][j] - pref[i - 1][j - 1] + (int) (a[i][j] == '1');
}
auto get_sum = [&](int x1, int y1, int x2, int y2) {
return pref[x2][y2] - pref[x2][y1 - 1] - pref[x1 - 1][y2] + pref[x1 - 1][y1 - 1];
};
vector<vector<int>> checked(n + 1, vector<int>(m + 1));
int z = 0;
auto check = [&](int h, int w) {
z++;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
if (a[i][j] == '0') continue;
if (i + h - 1 <= n and j + w - 1 <= m and get_sum(i, j, i + h - 1, j + w - 1) == h * w) {
for (int x = i; x < i + h; x++) {
for (int y = j; y < j + w; y++) {
checked[x][y] = z;
}
}
}
if (checked[i][j] < z) return false;
}
}
return true;
};
vector<int> best(n + 1, -1);
auto get = [&](int h) {
if (best[h] != -1) return best[h];
int lx = 1, rx = (h > 1 ? best[h - 1] : m);
best[h] = 0;
while (lx <= rx) {
int mid = (lx + rx) >> 1;
if (check(h, mid)) {
best[h] = mid;
lx = mid + 1;
} else {
rx = mid - 1;
}
}
return best[h];
};
int ans = 0;
for (int i = 1; i <= n; i++) ans = max(ans, get(i) * i);
cout << ans;
}
