#include <bits/stdc++.h>
#define all(i) (i).begin(), (i).end()
#define debug(x) cerr << "Line(" << __LINE__ << ") -> " << #x << " is " << x << endl
using namespace std;
template<typename T1, typename T2>
ostream& operator << (ostream &i, pair<T1, T2> j) {
return i << j.first << ' ' << j.second;
}
template<typename T>
ostream& operator << (ostream &i, vector<T> j) {
i << '{' << j.size() << ':';
for (T ii : j) i << ' ' << ii;
return i << '}';
}
typedef long long ll;
typedef pair<int, int> pi;
int main() {
ios::sync_with_stdio(0), cin.tie(0);
int n, m;
cin >> n >> m;
vector<string> v(n + 2, string(m + 2, '0'));
for (int i = 1; i <= n; ++i) for (int j = 1; j <= m; ++j) cin >> v[i][j];
vector<vector<int>> h(n + 2, vector<int>(m + 2, 0)), w(n + 2, vector<int>(m + 2, 0));
int _h = n, _w = m;
for (int i = n; i; --i) for (int j = m; j; --j) if (v[i][j] == '1') {
h[i][j] = h[i + 1][j] + 1, w[i][j] = w[i][j + 1] + 1;
if (v[i - 1][j] == '0') _h = min(_h, h[i][j]);
if (v[i][j - 1] == '0') _w = min(_w, w[i][j]);
}
vector<int> lim(_h + 2, _w);
for (int i = 1; i <= n; ++i) {
pi pre(0, 0);
for (int j = 1; j <= m + 1; ++j) {
if (v[i - 1][j] == '0' && v[i][j - 1] == '0') {
pre = pi(j, h[i][j]);
continue;
}
if (h[i][j] >= pre.second) continue;
lim[h[i][j] + 1] = min(lim[h[i][j] + 1], j - pre.first);
pre.second = h[i][j];
}
}
int ans = 0;
for (int i = 1; i <= _h; ++i) lim[i] = min(lim[i], lim[i - 1]), ans = max(ans, i * lim[i]);
cout << ans;
}
