#ifdef ONPC
#define _GLIBCXX_DEBUG
#endif
#pragma GCC optimize("O3")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#include <malloc.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template<typename T1, typename T2> istream& operator>>(istream& in, pair<T1, T2>& p) {in >> p.first >> p.second; return in;}
template<typename T1, typename T2> ostream& operator<<(ostream& out, pair<T1, T2>& p) {out << p.first << ' ' << p.second; return out;}
template<typename T> istream& operator>>(istream& in, vector<T>& v) {for (auto& x : v) in >> x; return in;}
template<typename T> ostream& operator<<(ostream& out, vector<T>& v) {for (auto& x : v) out << x << ' '; return out;}
template<typename T> ostream& operator<<(ostream& out, set<T>& v) {for (auto& x : v) out << x << ' '; return out;}
template<typename T> ostream& operator<<(ostream& out, multiset<T>& v) {for (auto& x : v) out << x << ' '; return out;}
const int MAX_INT = 2147483647;
const double pi = acos(-1.0);
const int mod = 1e9 + 7;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<vector<char>> f(n, vector<char>(m));
for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) cin >> f[i][j];
vector<vector<int>> up(n, vector<int>(m)), down(n, vector<int>(m));
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (f[i][j] == '0') {
up[i][j] = i;
} else {
up[i][j] = (i - 1 >= 0 ? up[i - 1][j] : i - 1);
}
}
}
for (int i = n - 1; i >= 0; i--) {
for (int j = 0; j < m; j++) {
if (f[i][j] == '0') {
down[i][j] = i;
} else {
down[i][j] = (i + 1 < n ? down[i + 1][j] : i + 1);
}
}
}
int mx_y = 1e9;
for (int j = 0; j < m; j++) {
for (int i = 0; i < n; i++) {
int mn = 1e9;
if (f[i][j] == '0') continue;
int r = i;
while (r + 1 < n && f[r + 1][j] == '1') r++;
mn = min(mn, r - i + 1);
i = r;
mx_y = min(mx_y, mn);
}
}
vector<ll> best(m + 1, mx_y);
int mx_x = 1e9;
for (int i = 0; i < n; i++) {
int mn = 1e9;
for (int j = 0; j < m; j++) {
if (f[i][j] == '0') continue;
int r = j;
while (r + 1 < m && f[i][r + 1] == '1') r++;
mn = min(mn, r - j + 1);
int u = -1;
int d = n;
for (int id = j, len = 1; id <= r; id++, len++) {
u = max(u, up[i][id]);
d = min(d, down[i][id]);
best[len] = min<ll>(best[len], d - u - 1);
}
j = r;
}
mx_x = min(mx_x, mn);
}
ll ans = 0;
for (int i = 1; i <= mx_x; i++) ans = max(ans, i * best[i]);
cout << ans << '\n';
return 0;
}
