#include<bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;
#define ll long long
#define rep(i,n,N) for(int i = n; i<=N; ++i)
#define rap(i,n,N) for(int i = n; i>=N; --i)
#define For(i,n,N) for(int i = n; i< N; ++i)
#define endl '\n'
#define pb push_back
#define all(x) x.begin(),x.end()
#define mems(x,y) memset(x,y,sizeof x)
#define ari(x) array<int,x>
#define pll pair<ll,ll>
#define pii pair<int,int>
#define fi first
#define se second
const int MAX = 2500 + 5;
mt19937 rng(time(NULL));
int n,m,mnr,mnc,cnt,y[MAX][MAX],z[MAX][MAX],ans;
char c;
bool x[MAX][MAX];
vector<ari(3)> v;
inline bool cek(int r,int c,int dr,int dc){
return y[r][c] - y[r-dr][c] - y[r][c-dc] + y[r-dr][c-dc] == dr*dc;
}
inline bool solve(int dr,int dc){
rep(i,1,n)mems(z[i], 0);
rep(i,dr,n)rep(j,dc,m)if(x[i][j] && cek(i,j,dr,dc)){
z[i][j]++;
z[i-dr][j]--;
z[i][j-dc]--;
z[i-dr][j-dc]++;
}
rap(i,n,1)rap(j,m,1){
z[i][j]+= z[i+1][j]+z[i][j+1]-z[i+1][j+1];
if((!!z[i][j])!=x[i][j])return 0;
}
return 1;
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin>>n>>m;
mnr = n, mnc = m;
rep(i,1,n){
rep(j,1,m){
cin>>c;
x[i][j] = c=='1';
y[i][j] = y[i-1][j]+y[i][j-1]-y[i-1][j-1]+x[i][j];
if(x[i][j])++cnt;
else if(cnt)mnc = min(mnc, cnt), cnt = 0;
}
if(cnt)mnc = min(mnc, cnt), cnt = 0;
}
rep(j,1,m){
rep(i,1,n){
if(x[i][j])++cnt;
else if(cnt)mnr = min(mnr, cnt), cnt = 0;
}
if(cnt)mnr = min(mnr, cnt), cnt = 0;
}
if(solve(mnr, mnc))return cout<<mnr*mnc<<endl,0;
if(n*m > 2e6){
int k = min(mnr, mnc);
int le,ri,mid;
le = 1, ri = k;
while(le<=ri){
mid = le+ri>>1;
if(solve(mid, mid))k = mid, le = mid+1;
else ri = mid-1;
}
int r,c;
r = c = k;
if(r+1<=mnr && solve(r+1, c)){
++r;
le = r+1, ri = mnr;
while(le<=ri){
mid = le+ri>>1;
if(solve(mid, c))r = mid, le = mid+1;
else ri = mid-1;
}
}
else if(c+1<=mnc){
le = c+1, ri = mnc;
while(le<=ri){
mid = le+ri>>1;
if(solve(r, mid))c = mid, le = mid+1;
else ri = mid-1;
}
}
cout<<r*c<<endl;
return 0;
}
ans = mnc;
rep(i,2,mnr){
while(i*mnc>ans && !solve(i, mnc))--mnc;
ans = max(ans, i*mnc);
}
cout<<ans<<endl;
return 0;
}
