#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#pragma GCC optimize("-O3")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#define pb push_back
#define fr(i, l, r) for(ll i = l; i <= r; ++ i)
#define rf(i, l, r) for(ll i = l; i >= r; -- i)
using namespace std;
using namespace __gnu_pbds;
template <typename T>
using _set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef int ll;
typedef pair<ll, ll> pll;
const ll oo = ll(1e9) + 10;
ll p[3000][300];
ll get(ll x1, ll y1, ll x2, ll y2){
return p[x2][y2] - p[x2][y1 - 1] - p[x1 - 1][y2] + p[x1 - 1][y1 - 1];
}
int main() {
ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
ll n, m, ansx = 0, ansy = 0, ans = 0;
cin >> n >> m;
if(n * m > 10000)return 0;
char a[n + 1][m + 1];
fr(i, 1, n)fr(j, 1, m){
cin >> a[i][j];
p[i][j] = p[i - 1][j] + p[i][j - 1] - p[i - 1][j - 1] + 1 - (a[i][j] - '0');
}
rf(r, n, 1){
rf(c, m, 1){
vector <pll> v;
fr(i, 1, n - r + 1){
fr(j, 1, m - c + 1){
//if(a[i][j] == '0')continue;
//cout << "i = " << i << " j = " << j << " get = " << get(i, j, i + r - 1, j + c - 1) << endl;
if(get(i, j, i + r - 1, j + c - 1) == 0)v.pb({i, j});
}
}
reverse(v.begin(), v.end());
//cout << "r = " << r << " c = " << c << endl;
//cout << "v: " << endl;
//for(auto i : v)cout << i.first << ' ' << i.second << endl;
bool usd[n + 1][m + 1];
fr(i, 1, n)fr(j, 1, m)usd[i][j] = 0;
for(auto x : v){
fr(i, 0, r - 1){
if(usd[x.first + i][x.second])break;
fr(j, 0, c - 1){
if(usd[x.first + i][x.second + j])break;
usd[x.first + i][x.second + j] = 1;
}
}
}
bool ok = 1;
fr(i, 1, n){
fr(j, 1, m){
if(a[i][j] == '1' && usd[i][j] == 0)ok = 0;
}
}
if(ok)ans = max(ans, r * c);
}
}
//cout << ansx << ' ' << ansy << endl;
cout << ans;
}
/*
3 3
011
111
111
*/
