#include <bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define ub upper_bound
#define lb lower_bound
#define ll long long
#define ld long double
#define pii pair<int, int>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(),x.rend()
#define prc(n) fixed << setprecision(n)
#define fastios ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define pi acos(-1);
const int inf = 1e9+7;
const int N = 2505;
int a[N][N], mnc, mnr, d[N][N], u[N][N], ans[N];
void solve(){
mnr = inf, mnc = inf;
int n, m;
cin>>n>>m;
for(int i=1;i<=n;i++){
for(int j=1;j<=m;j++){
char c;
cin>>c;
a[i][j] = c - '0';
}
}
for(int i=1;i<=n;i++){
for(int j=1;j<=m;j++){
if(a[i][j])u[i][j] = u[i-1][j] + 1;
}
}
for(int i=n;i>0;i--){
for(int j=1;j<=m;j++){
if(a[i][j]){
d[i][j] = d[i+1][j]+1;
if(a[i+1][j] == 0) mnc = min(mnc, u[i][j]);
}
}
}
for(int i=1;i<=m;i++) ans[i] = mnc;
for(int i=1;i<=n;i++){
int aa = inf, b = inf, c = 0;
for(int j=1;j<=m;j++){
if(a[i][j] == 0){
if(c!=0) mnc = min(c, mnc);
aa = b = inf, 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 = inf, b = inf, c = 0;
for(int j = m; j>0; j--){
if(a[i][j] == 0){
if(c!=0) mnr = min(mnr, c);
aa = b = inf, 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;
for(int i=1;i<=mnr;i++){
mx = max(ans[i] * i, mx);
}
cout<<mx<<"\n";
return;
}
int main(){
fastios
int t = 1;
//cin>>t;
while(t--) solve();
return 0;
}
