#include<bits/stdc++.h>
using namespace std;
int a,b,c,d,e,i,j,dp[2509][2509],zx,xc,qw,we,k[2509][2509],pas,dd;
string s;
bool f[2509][2509];
int main(){
ios_base::sync_with_stdio(false),cin.tie(0),cout.tie(0);
cin>>a>>b;
for(c=1; c<=a; c++){
cin>>s;
for(d=1; d<=b; d++){
f[c][d]=s[d-1]-'0';
}
}
for(c=1; c<=a; c++){
for(d=1; d<=b; d++) dp[c][d]=dp[c-1][d]+dp[c][d-1]-dp[c-1][d-1]+f[c][d];
}
d=b;
for(c=1; c<=a; c++){
while(d>=1){
// cout<<c<<" "<<d<<endl;
bool bo=0;
for(i=1; i<=a; i++) for(j=1; j<=b; j++) k[i][j]=0;
for(i=c; i<=a; i++){
for(j=d; j<=b; j++){
qw=i-c+1;we=j-d+1;
if(dp[i][j]-dp[i][we-1]-dp[qw-1][j]+dp[qw-1][we-1]==c*d){
k[qw][we]=1;
}
}
}
/* if(c==1&&d==5){
for(i=1; i<=a; i++){
for(j=1; j<=b; j++) cout<<k[i][j]<<" ";
cout<<endl;
}
}
if(c==1&&d==5) cout<<endl<<endl<<endl<<endl<<endl<<endl<<endl;*/
for(i=1; i<=a; i++){
for(j=1; j<=b; j++) k[i][j]=k[i-1][j]+k[i][j-1]-k[i-1][j-1]+k[i][j];
}
/* if(c==1&&d==5){
for(i=1; i<=a; i++){
for(j=1; j<=b; j++) cout<<k[i][j]<<" ";
cout<<endl;
}
}*/
for(i=1; i<=a; i++){
if(bo==1) break;
for(j=1; j<=b; j++){
if(f[i][j]==0) continue;
qw=i-c+1;we=j-c+1;
if(qw<0) qw=0;
if(we<0) we=0;
int hj=0;
if(qw!=0&&we!=0) hj=k[i][j]-k[qw-1][j]-k[i][we-1]+k[qw-1][we-1]; else hj=k[i][j];
if(hj==0){
bo=1;
break;
}
}
}
if(bo==0){
if(pas<c*d) pas=c*d;
break;
}
d--;
}
}
cout<<pas;
return 0;
}
