#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define foru(i, l, r) for(int i = l; i <= r; i++)
#define ford(i, r, l) for(int i = r; i >= l; i--)
#define __TIME (1.0 * clock() / CLOCKS_PER_SEC)
typedef pair<int, int> ii;
typedef pair<ii, int> iii;
typedef pair<ii, ii> iiii;
const int N = 2500+ 5;
const int oo = 1e9, mod = 1e9 + 7;
int a[N][N], u[N][N], d[N][N], ans[N];
void process() {
int mnr = oo, mnc = oo;
int n, m;
cin >> n >> m;
foru(i,1,n) {
foru(j,1,m) {
char c;
cin >> c;
a[i][j] = c - '0';
}
}
foru(i,1,n) {
foru(j,1,m) {
if (a[i][j]) u[i][j] = u[i - 1][j] + 1;
}
}
for (int i = n; i > 0; i--) {
foru(j,1,m) {
if (a[i][j]) {
d[i][j] = d[i + 1][j] + 1;
if (a[i + 1][j] == 0) mnc = min(mnc, u[i][j]);
}
}
}
foru(i,1,m) ans[i] = mnc;
foru(i,1,n) {
int aa = oo, b = oo, c = 0;
foru(j,1,m) {
if (a[i][j] == 0) {
if (c != 0) mnc = min(c, mnc);
aa = b = oo, c = 0;
} else {
aa = min(aa, d[i][j]);
b = min(b, u[i][j]);
c++;
ans[c] = min(ans[c], b + aa - 1);
}
}
aa = oo, b = oo, c = 0;
ford(j,m,0) {
if (a[i][j] == 0) {
if (c != 0) mnr = min(mnr, c);
aa = b = oo, c = 0;
} else {
aa = min(d[i][j], aa);
b = min(u[i][j], b);
c++;
ans[c] = min(ans[c], b + aa - 1);
}
}
if (c > 0) mnr = min(mnr, c);
}
int mx = 0;
foru(i,1,mnr) {
mx = max(ans[i] * i, mx);
}
cout << mx << "\n";
return;
}
signed main() {
cin.tie(0)->sync_with_stdio(false);
//freopen(".inp", "r", stdin);
//freopen(".out", "w", stdout);
process();
cerr << "Time elapsed: " << __TIME << " s.\n";
return 0;
}
// dont stop
