#include<bits/stdc++.h>
using namespace std;
#ifndef BADGNU
#pragma GCC target("sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#endif
#pragma GCC optimize("Ofast,unroll-loops,fast-math,O3")
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define ll long long
// #define int ll
#define ld long double
#define y1 cheza
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
template<class T> using ordered_multiset = tree<T,null_type,less_equal<T>,rb_tree_tag,tree_order_statistics_node_update>;
const int N=2600;
const int M=5001;
const int B=447;
const int mod=998244353;
const ll INF=1e18;
const int dx[]={1,-1,0,0};
const int dy[]={0,0,1,-1};
const double eps=1e-6;
int n,m;
int a[N][N];
int L[N][N],R[N][N];
int y[N];
void test(){
cin>>n>>m;
for(int i=0;i<=n;i++){
y[i]=m+1;
}
for(int i=1;i<=n;i++){
for(int j=1;j<=m;j++){
char x;
cin>>x;
a[i][j]=x-'0';
}
}
for(int i=1;i<=n;i++){
int cur=0;
for(int j=1;j<=m;j++){
if(a[i][j]){
L[i][j]=L[i][j-1]+1;
}
else{
L[i][j]=0;
}
}
for(int j=m;j>=1;j--){
if(a[i][j]){
R[i][j]=R[i][j+1]+1;
}
else{
R[i][j]=0;
}
}
for(int j=1;j<=m;j++){
if(a[i][j]){
y[1]=min(y[1],L[i][j]+R[i][j]-1);
}
}
}
int x=n;
for(int j=1;j<=m;j++){
int tl=m;
int tr=m;
int res=0;
for(int i=1;i<=n;i++){
if(a[i][j]){
res++;
tl=min(tl,L[i][j]);
tr=min(tr,R[i][j]);
y[res]=min(y[res],tr+tl-1);
}
else{
if(res>0){
x=min(x,res);
}
res=0;
tl=m;
tr=m;
}
}
if(res>0){
x=min(x,res);
}
res=0;
tl=m;
tr=m;
for(int i=n;i>=1;i--){
if(a[i][j]){
res++;
tl=min(tl,L[i][j]);
tr=min(tr,R[i][j]);
y[res]=min(y[res],tr+tl-1);
}
else{
if(res>0){
x=min(x,res);
}
res=0;
tl=m;
tr=m;
}
}
if(res>0){
x=min(x,res);
}
}
int ans=0;
for(int i=1;i<=x;i++){
y[i]=min(y[i-1],y[i]);
ans=max(ans,i*y[i]);
}
cout<<ans<<'\n';
}
/*
*/
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
// cout.tie(nullptr);
int t2=1;
// cin>>t2;
for(int i=1;i<=t2;i++){
test();
}
}
