#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fi first
#define se second
#define ll long long
#define ld long double
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define mpp make_pair
#define ve vector
using namespace std;
using namespace __gnu_pbds;
template<class T> using oset = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
const ll inf = 1e18; const int iinf = 1e9;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T> inline bool chmin(T& a, T b) { return (a > b ? a = b, 1 : 0); }
template <typename T> inline bool chmax(T& a, T b) { return (a < b ? a = b, 1 : 0); }
inline void solve() {
int n, m;
cin >> n >> m;
ve<ve<int>> a(n, ve<int>(m));
for (int i = 0; i < n; ++i) {
for (int j = 0; j < m; ++j) {
char x;
cin >> x;
a[i][j] = x - '0';
}
}
ve<int> mx(m + 2, iinf);
for (int rep = 0; rep < 2; ++rep) {
ve<ve<int>> dp1(n, ve<int> (m)), dp2(n, ve<int> (m));
for (int j = 0; j < m; ++j) {
for (int i = 0; i < n; ++i) {
dp1[i][j] = (a[i][j] ? 1 + (!i ? 0 : dp1[i - 1][j]) : 0);
}
for (int i = n - 1; ~i; --i) {
dp2[i][j] = (a[i][j] ? 1 + (i + 1 == n ? 0 : dp2[i + 1][j]) : 0);
if (a[i][j]) chmin(mx[1], dp1[i][j] + dp2[i][j] - 1);
}
}
for (int i = 0; i < n; ++i) {
for (int j = 0; j < m; ) {
if (!a[i][j]) { ++j; continue; }
int p = j;
while (j < m && a[i][p]) ++p;
int a = iinf, b = iinf;
for (int k = j; k < p; ++k) {
chmin(a, dp1[i][k]); chmin(b, dp2[i][k]);
chmin(mx[k - j + 1], a + b - 1);
}
chmin(mx[p - j + 1], 0);
j = p;
}
}
for (int i = 0; i < n; ++i) reverse(all(a[i]));
}
ll ans = 0;
for (int i = 1; i <= m; ++i) {
chmin(mx[i], mx[i - 1]);
chmax(ans, i * 1ll * mx[i]);
}
cout << ans;
}
signed main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
int q = 1; // cin >> q;
while (q--) solve();
cerr << fixed << setprecision(3) << "Time execution: " << (double)clock() / CLOCKS_PER_SEC << endl;
}
