#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
void debug_out() {cerr<<endl;}
template <typename Head, typename... Tail>
void debug_out(Head _H, Tail... _T) {cerr<<" "<<to_string(_H);debug_out(_T...);}
#define debug(...) cerr<<"["<<#__VA_ARGS__<<"]:",debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif
const int MAXN = 2005;
const int inf=1000000500ll;
const long long oo =1000000000000000500ll;
const int MOD = (int)1e9;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef pair<int,int> pi;
vector<int> row[MAXN], col[MAXN];
struct ufds_{
int p[MAXN];
ufds_(){
iota(p,p+MAXN,0);
}
int find(int x){
if(x==p[x])return x;
else return p[x]=find(p[x]);
}
void merge(int x, int y){
x=find(x);y=find(y);
p[y]=x;
}
}ufds;
int dx[]={-1,0,1,0};
int dy[]={0,1,0,-1};
int n;
int get(int x, int y){
return x*n+y;
}
int biggest_stadium(int N, std::vector<std::vector<int>> V)
{
n=N;
int cnt=0;
for(int i=0;i<n;i++){
for(int j=0;j<n;j++){
if(V[i][j] == 0){
++cnt;
for(int k=0;k<3;k++){
int nx=i+dx[k];
int ny=j+dy[k];
if(nx<0 || nx>=n ||ny<0 || ny>=n || V[nx][ny])continue;
ufds.merge(get(i,j),get(nx,ny));
}
}
}
}
unordered_set<int>os;
for(int i=0;i<n;i++){
for(int j=0;j<n;j++){
if(V[i][j] == 0)os.insert(ufds.find(get(i,j)));
}
}
if(os.size() > 1)return 0;
for(int i=0;i<n;i++){
for(int j=0;j<n;j++){
if(V[i][j])row[i].push_back(j);
}
}
for(int i=0;i<n;i++){
for(int j=0;j<n;j++){
if(V[i][j])col[j].push_back(i);
}
}
for(int i=0;i<n;i++){
for(int j=0;j<n;j++){
if(V[i][j] == 0){
if(upper_bound(row[i].begin(),row[i].end(),j) != row[i].end() && upper_bound(col[j].begin(),col[j].end(),i) != col[j].end()){
int nx=*upper_bound(row[i].begin(),row[i].end(),j);
int ny=*upper_bound(col[j].begin(),col[j].end(),i);
if(V[nx][ny] == 0)return 0;
}
if(upper_bound(row[i].begin(),row[i].end(),j) != row[i].end() && lower_bound(col[j].begin(),col[j].end(),i) != col[j].begin()){
int nx=*upper_bound(row[i].begin(),row[i].end(),j);
int ny=*prev(lower_bound(col[j].begin(),col[j].end(),i));
if(V[nx][ny] == 0)return 0;
}
if(lower_bound(row[i].begin(),row[i].end(),j) != row[i].begin() && upper_bound(col[j].begin(),col[j].end(),i) != col[j].end()){
int nx=*prev(lower_bound(row[i].begin(),row[i].end(),j));
int ny=*upper_bound(col[j].begin(),col[j].end(),i);
if(V[nx][ny] == 0)return 0;
}
if(lower_bound(row[i].begin(),row[i].end(),j) != row[i].begin() && lower_bound(col[j].begin(),col[j].end(),i) != col[j].begin()){
int nx=*prev(lower_bound(row[i].begin(),row[i].end(),j));
int ny=*prev(lower_bound(col[j].begin(),col[j].end(),i));
if(V[nx][ny] == 0)return 0;
}
}
}
}
return cnt;
}
