#include <bits/stdc++.h>
#define fi first
#define se second
#define mp make_pair
#define TASK ""
#define ALL(x) (x).begin(), (x).end()
using namespace std;
template <typename T1, typename T2> bool mini(T1 &a, T2 b) {
if (a > b) {a = b; return true;} return false;
}
template <typename T1, typename T2> bool maxi(T1 &a, T2 b) {
if (a < b) {a = b; return true;} return false;
}
const int N = 2505;
const int oo = 1e9;
const long long ooo = 1e18;
const int mod = 1e9 + 7; // 998244353;
const long double pi = acos(-1);
int up[N][N];
int dn[N][N];
int a[N][N];
int mx[N];
int n,m;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
#ifdef ONLINE_JUDGE
// freopen(TASK".inp","r",stdin);
// freopen(TASK".out","w",stdout);
#endif
cin >> n >> m;
for (int i = 1; i <= n; i++) {
string str; cin >> str;
for (int j = 1; j <= m; j++)
a[i][j] = str[j - 1] - '0';
}
for (int j = 1; j <= m; j++) {
for (int i = 1; i <= n; i++)
if (a[i][j])
up[i][j] = up[i - 1][j] + 1;
for (int i = n; i >= 1; i--)
if (a[i][j])
dn[i][j] = dn[i + 1][j] + 1;
}
for (int i = 1; i <= m; i++)
mx[i] = oo;
for (int i = 1; i <= n; i++)
for (int t = 0; t < 2; t++) {
for (int j = 1; j <= m; j++) if (a[i][j]) {
int k = j;
while (a[i][k])
k++;
int f = oo, g = oo;
for (int it = j; it < k; it++) {
mini(f, up[i][it]);
mini(g, dn[i][it]);
// cerr << i << " " << j << " " << it << " " << f << " " << g << "\n";
mini(mx[it - j + 1], f + g - 1);
}
mini(mx[k - j + 1], 0);
j = k;
}
reverse(a[i] + 1, a[i] + m + 1);
reverse(dn[i] + 1, dn[i] + m + 1);
reverse(up[i] + 1, up[i] + m + 1);
}
int ans = 0;
for (int i = 1; i <= m; i++) {
if (mx[i] == 0)
break;
maxi(ans, i * mx[i]);
}
cout << ans;
return 0;
}
