#include <bits/stdc++.h>
using namespace std;
const int NM = 2500, inf = 1e9+7;
int N, M, Up[NM+5][NM+5], Down[NM+5][NM+5], Left[NM+5][NM+5], Right[NM+5][NM+5], H = +inf, W = +inf;
int mx[NM+5], ans = 0;
char a[NM+5][NM+5];
void preprocess(){
for (int i = 1; i <= N; i++)
for (int j = 1; j <= M; j++)
if (a[i][j] == '1'){
Up[i][j] = Up[i-1][j]+1;
Left[i][j] = Left[i][j-1]+1;
}
for (int i = N; i >= 1; i--)
for (int j = M; j >= 1; j--)
if (a[i][j] == '1'){
Down[i][j] = Down[i+1][j]+1;
Right[i][j] = Right[i][j+1]+1;
H = min(H, Up[i][j]+Down[i][j]-1);
W = min(W, Left[i][j]+Right[i][j]-1);
}
for (int i = 1; i <= H; i++) mx[i] = +inf;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> N >> M;
for (int i = 1; i <= N; i++)
for (int j = 1; j <= M; j++)
cin >> a[i][j];
preprocess();
for (int i = 1; i <= N; i++)
for (int j = 1; j <= M; j++){
if (Down[i][j] == 1){
int l = -inf, r = +inf;
for (int k = 1; k <= H; k++){
if (i-k+1 < 1) continue;
l = max(l, j-Left[i-k+1][j]+1);
r = min(r, j+Right[i-k+1][j]-1);
mx[k] = min(mx[k], r-l+1);
}
}
if (Up[i][j] == 1){
int l = -inf, r = +inf;
for (int k = 1; k <= H; k++){
if (i+k-1 > N) continue;
l = max(l, j-Left[i+k-1][j]+1);
r = min(r, j+Right[i+k-1][j]-1);
mx[k] = min(mx[k], r-l+1);
}
}
}
for (int i = 1; i <= H; i++) ans = max(ans, i*mx[i]);
cout << ans;
return 0;
}
