#include <bits/stdc++.h>
//#define int long long
using namespace std;
struct Alien {
int t, id;
};
const int N = 2500 + 42, INF = 1e9 + 42;
bool alien[N*N];
vector<Alien> add;
int n, m, t[N], sz[N*N];
int F(int i) {
if(sz[i] < 0)
return i;
return sz[i] = F(sz[i]);
}
inline int getSz(int i) {
return -sz[F(i)];
}
void U(int a, int b) {
a = F(a), b = F(b);
if(a == b)
return;
if(-sz[a] < -sz[b])
swap(a, b);
sz[a] += sz[b];
sz[b] = a;
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
for(int i = 0; i < N*N; i++)
sz[i] = -1;
cin >> n >> m;
n++, m++;
for(int i = 1; i < n; i++)
for(int j = 1; j < m; j++) {
char c; cin >> c;
alien[m * i + j] = (c == '1');
}
int minLen = INF;
for(int i = 1; i < n; i++)
for(int j = 1; j < m; j++)
if(alien[m * i + j]) {
int id = m * i + j;
t[j] = t[j-1] + 1;
alien[id] = false;
add.push_back({t[j], id});
if(!alien[id+1])
minLen = min(minLen, t[j]);
} else {
t[j] = 0;
}
sort(add.begin(), add.end(),
[](Alien a, Alien b) {
if(a.t == b.t)
return a.id < b.id;
return a.t > b.t;
});
multiset<int> len;
int ans = 0, l = (int)add.size();
for(int i = 0; i < l; i++) {
int j = add[i].id;
alien[j] = true;
if(alien[j - m]) {
len.erase(len.find(getSz(j - m)));
U(j - m, j);
}
if(alien[j + m]) {
len.erase(len.find(getSz(j + m)));
U(j + m, j);
}
len.insert(getSz(j));
if(add[i].t <= minLen && (i == l-1 || add[i+1].t < add[i].t)) {
auto it = len.begin();
ans = max(ans, (*it) * add[i].t);
}
}
cout << ans;
}
