//
// Created by liasa on 15/11/2025.
//
#include <bits/stdc++.h>
using namespace std;
#define ll int
#define vll vector<ll>
#define loop(i, s, e) for (ll i = s; i < e; ++i)
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
ll n, m;
cin >> n >> m;
vector<vll> grid(n, vll(m));
bool cnt = 0;
loop(i, 0, n) {
string s;
cin >> s;
loop(j, 0, m) {
grid[i][j] = (s[j] - '0');
if (grid[i][j])
cnt = 1;
}
}
if (!cnt) {
cout << 0;
return 0;
}
vector<vll> up(n, vll(m)), dn(n, vll(m));
loop(j, 0, m) {
loop(i, 0, n) {
if (grid[i][j])
up[i][j] = (i ? up[i - 1][j] : 0) + 1;
else
up[i][j] = 0;
}
for (ll i = n - 1; i >= 0; --i) {
if (grid[i][j])
dn[i][j] = (i + 1 < n ? dn[i + 1][j] : 0) + 1;
else
dn[i][j] = 0;
}
}
vll ans(m + 1, n);
loop(i, 0, n) {
for (ll j = 0; j < m;) {
if (!grid[i][j]) {
j++;
continue;
}
ll L = j, min_up = -1e9, min_down = 1e9, k = j;
while (k < m && grid[i][k]) {
min_up = max(min_up, i - up[i][k] + 1);
min_down = min(min_down, i + dn[i][k] - 1);
ll w = k - L + 1;
ll cap = min_down - min_up + 1;
if (cap < 0)
cap = 0;
ans[w] = min(ans[w], cap);
k++;
}
ll len = k - L;
if (len + 1 <= m)
ans[len + 1] = 0;
j = k;
}
}
loop(i, 0, n) {
for (ll j = m - 1; j >= 0;) {
if (!grid[i][j]) {
j--;
continue;
}
ll R = j, min_up = -1e9, min_down = 1e9, k = j;
while (k >= 0 && grid[i][k]) {
min_up = max(min_up, i - up[i][k] + 1);
min_down = min(min_down, i + dn[i][k] - 1);
ll w = R + 1 - k;
ll B = min_down - min_up + 1;
if (B < 0)
B = 0;
ans[w] = min(ans[w], B);
k--;
}
ll len = R - k;
if (len + 1 <= m)
ans[len + 1] = 0;
j = k;
}
}
for (ll w = 1; w <= m; ++w)
ans[w] = min(ans[w], ans[w - 1]);
ll res = 0;
for (ll w = 1; w <= m; ++w)
res = max(res, w * ans[w]);
cout << res;
}
