//#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#define rc(x) return cout<<x<<endl,0
#define pb push_back
#define mkp make_pair
#define in insert
#define er erase
#define fd find
#define fr first
#define sc second
typedef long long ll;
typedef long double ld;
const ll INF=0x3f3f3f3f3f3f3f3f;
const ll llinf=(1LL<<62);
const int inf=(1<<30);
const int nmax=2505;
const int mod=1e9+7;
using namespace std;
int n,m,i,j,cur,h[nmax][nmax],v[nmax][nmax],x,y,a[nmax][nmax],ad[nmax][nmax],b[nmax][nmax],rs,mid,l,r;
char c;
bool ok(int h,int w)
{
int i,j,x;
for(i=1;i<=n;i++)for(j=1;j<=m;j++)ad[i][j]=0;
for(i=1;i<=n;i++)
{
for(j=1;j<=m;j++)
{
if(i<=n-h+1 && j<=m-w+1)
{
x=b[i+h-1][j+w-1]-b[i+h-1][j-1]-b[i-1][j+w-1]+b[i-1][j-1];
if(x==h*w)
{
ad[i][j]++;
ad[i][j+w]--;
ad[i+h][j]--;
ad[i+h][j+w]++;
}
}
ad[i][j]+=ad[i-1][j]+ad[i][j-1]-ad[i-1][j-1];
if(!ad[i][j] && a[i][j])return 0;
}
}
return 1;
}
int main()
{
//freopen("sol.in","r",stdin);
//freopen("sol.out","w",stdout);
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ios_base::sync_with_stdio(false);cin.tie(0);cerr.tie(0);cout.tie(0);
cin>>n>>m;
for(i=1;i<=n;i++)
{
for(j=1;j<=m;j++)
{
cin>>c;
a[i][j]=(c=='1');
b[i][j]=a[i][j]+b[i-1][j]+b[i][j-1]-b[i-1][j-1];
}
}
x=y=inf;
for(i=1;i<=n;i++)
{
for(j=m;j>=1;j--)
{
if(a[i][j])
{
h[i][j]=h[i][j+1]+1;
if(!a[i][j-1])y=min(y,h[i][j]);
}
}
}
for(i=1;i<=m;i++)
{
for(j=n;j>=1;j--)
{
if(a[j][i])
{
v[j][i]=v[j+1][i]+1;
if(!a[j-1][i])x=min(x,v[j][i]);
}
}
}
if(x==inf)rc(0);
if(n*m>=1e6)rc(x*y);
for(i=1;i<=x;i++)
{
l=1,r=y,cur=0;
while(l<=r)
{
mid=(l+r)/2;
if(ok(i,mid))cur=mid,l=mid+1;
else r=mid-1;
}
rs=max(rs,i*cur);
}
cout<<rs<<endl;
return 0;
}
