#include<bits/stdc++.h>
using namespace std;
const int MAX = 2500 + 5;
int n,m,x[MAX][MAX],pf[MAX][MAX],atk[MAX][MAX];
char c;
int get(int x1,int y1,int x2,int y2){
x1--, y1--;
return pf[x2][y2] - pf[x2][y1] - pf[x1][y2] + pf[x1][y1];
}
bool bisa(int h,int w){
memset(atk, 0, sizeof atk);
for(int i = h; i<=n; i++){
for(int j = w; j<=m; j++){
if(get(i-h+1, j-w+1, i, j) == h*w){
atk[i-h+1][j-w+1]++;
atk[i-h+1][j+1]--;
atk[i+1][j-w+1]--;
atk[i+1][j+1]++;
}
}
}
for(int i = 1; i<=n; i++){
for(int j = 1; j<=m; j++){
atk[i][j] = atk[i-1][j] + atk[i][j-1] - atk[i-1][j-1] + atk[i][j];
if(atk[i][j]){
if(!x[i][j])return false;
}
else {
if(x[i][j])return false;
}
}
}
return true;
}
int main(){
ios_base::sync_with_stdio(false);
cin>>n>>m;
for(int i = 1; i<=n; i++){
for(int j = 1; j<=m; j++){
cin>>c;
x[i][j] = (c=='1');
pf[i][j] = pf[i-1][j] + pf[i][j-1] - pf[i-1][j-1] + x[i][j];
}
}
// bisa(3, 1);
//
// for(int i = 1; i<=n; i++){
// for(int j = 1; j<=m; j++){
// cout<<atk[i][j]<<" ";
// }
// cout<<endl;
// }
int ans = 0;
int w,h;
int le,ri,mid,s;
le = 2, ri = min(n,m);
s = 1;
while(le<=ri){
mid = (le+ri)>>1;
if(bisa(mid, mid))s = mid, le = mid+1;
else ri = mid-1;
}
h = w = s;
if(w+1<=m && bisa(h,w+1)){
le = w+1, ri = m;
while(le<=ri){
mid = (le+ri)>>1;
if(bisa(h, mid))w = mid, le = mid+1;
else ri = mid-1;
}
}
else if(h+1<=n){
le = h+1, ri = n;
while(le<=ri){
mid = (le+ri)>>1;
if(bisa(mid, w))h = mid, le = mid+1;
else ri = mid-1;
}
}
cout<<h*w<<endl;
return 0;
}
