#pragma GCC optimize("Ofast","O3","unroll-loops")
#pragma GCC target("avx","avx2")
#include <bits/stdc++.h>
using namespace std;
#define LCBorz ios_base::sync_with_stdio(false); cin.tie(0);
#define all(x) x.begin(), x.end()
#define endl '\n'
const int N=200005;
int32_t main() {
LCBorz;
int n,m;cin>>n>>m;
vector<vector<int>> v(n+1,vector<int>(m+1,0)),v1(n+1,vector<int>(m+1,0));
for(int i=1;i<=n;i++){
for(int j=1;j<=m;j++){
char c;cin>>c;
v[i][j]=v1[i][j]=(c=='0');
}
}
for(int i=1;i<=n;i++){
for(int j=1;j<=m;j++){
v1[i][j]+=v1[i-1][j]+v1[i][j-1]-v1[i-1][j-1];
}
}
int ans=0;
int last=0;
auto check=[&](int a,int b)->int {
vector<vector<int>> pre(n+2,vector<int>(m+2,0));
for(int i=a;i<=n;i++){
for(int j=b;j<=m;j++){
if(v1[i][j]-v1[i][j-b]-v1[i-a][j]+v1[i-a][j-b]==0){
pre[i-a+1][j-b+1]++;
pre[i+1][j-b+1]--;
pre[i-a+1][j+1]--;
pre[i+1][j+1]++;
}
}
}
int flag=1;
for(int i=1;i<=n;i++){
for(int j=1;j<=m;j++){
pre[i][j]+=pre[i-1][j]+pre[i][j-1]-pre[i-1][j-1];
if(v[i][j]==0&&pre[i][j]==0){
flag=0;
}
}
}
return flag;
};
for(int i=n;i>=1;i--){
while(last+1<=m&&check(i,last+1)){
last++;
}
ans=max(ans,last*i);
}
cout<<ans<<endl;
return 0;
}
