#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define INF (long long)(2e15)
#define mod2 998244353
#define mod 1000000007
#define eps 1e-9
#define abs(x) ((x)>=0?(x):-(x))
#define y1 solai
#define fi first
#define se second
typedef int ll;
typedef long double ld;
typedef pair<ll,ll> pll;
typedef pair<double,double> pdd;
typedef pair<pll, ll> plll;
mt19937 rng(29);
const ll N=3100;
ll n,m,a[N][N],h,w,u[N][N],sum[N][N],ans;
string s;
ll get(ll x, ll y)
{
return sum[x+h-1][y+w-1]-sum[x-1][y+w-1]-sum[x+h-1][y-1]+sum[x-1][y-1];
}
ll f()
{
for(ll i=1;i<=n;i++)
for(ll j=1;j<=m;j++)
u[i][j]=0;
for(ll i=1;i<=n;i++)
for(ll j=1;j<=m;j++)
{
if(i+h-1<=n&&j+w-1<=m&&get(i,j)==h*w)
{
u[i][j]++;
u[i+h][j+w]++;
u[i+h][j]--;
u[i][j+w]--;
}
u[i][j]+=u[i-1][j]+u[i][j-1]-u[i-1][j-1];
if(a[i][j]&&!u[i][j])
return 0;
}
return 1;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cin>>n>>m;
h=n;
w=m;
for(ll i=1;i<=n;i++)
{
cin>>s;
for(ll j=1;j<=m;j++)
{
a[i][j]=s[j-1]-'0';
sum[i][j]=a[i][j]+sum[i-1][j]+sum[i][j-1]-sum[i-1][j-1];
}
}
w=m;
for(h=1;h<=n;h++)
{
while(w>ans/h&&!f())
w--;
ans=max(ans,h*w);
}
cout<<ans;
}
/*
5 6
001000
111110
111110
111110
000100
*/
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