#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(99);
int n,m,mnr,mnc,cnt,y[MAX][MAX],z[MAX][MAX];
char c;
bool x[MAX][MAX];
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;
}
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;
}
rep(i,mnr,n)rep(j,mnc,m)if(x[i][j] && cek(i,j,mnr,mnc)){
z[i][j]++;
z[i-mnr][j]--;
z[i][j-mnc]--;
z[i-mnr][j-mnc]++;
}
rap(i,n,1)rap(j,m,1)z[i][j]+= z[i+1][j]+z[i][j+1]-z[i+1][j+1];
rep(i,1,n){
// if(i==1)cout<<"--------------\n";
// rep(j,1,m)cout<<z[i][j];
// cout<<endl;
rep(j,1,m){
if((!!z[i][j])!=x[i][j]){
assert(x[i][j]);
}
}
}
cout<<mnr*mnc<<endl;
return 0;
}
