code:

#include<bits/stdc++.h>
#include<queue>
#define ll long long
#define ull unsigned long long
using namespace std;
struct node{
	int x,y;
};
char mapp[1005][1005];
char tmp[1005][1005];
int n;
queue<node> q;
int dx[4]={0,0,1,-1};
int dy[4]={1,-1,0,0};
void bfs(int x6,int y6){
	q.push(node{x6,y6});
	mapp[x6][y6]='$';
	int kx,ky;
	int xx,yy;
	while(!q.empty()){
		node kkk=q.front();
		q.pop();
		kx=kkk.x; ky=kkk.y;
		for(int i=0;i<4;i++){
			xx=kx+dx[i];
			yy=ky+dy[i];
			if(mapp[xx][yy]=='#'&&xx>=0&&yy>=0&&xx<n&&yy<n){
				mapp[xx][yy]='$';
				q.push(node{xx,yy});
			}
		}
	}
}
void bfs1(int x6,int y6){
	q.push(node{x6,y6});
	tmp[x6][y6]='$';
	int kx,ky;
	int xx,yy;
	while(!q.empty()){
		node kkk=q.front();
		q.pop();
		kx=kkk.x; ky=kkk.y;
		for(int i=0;i<4;i++){
			xx=kx+dx[i];
			yy=ky+dy[i];
			if(tmp[xx][yy]=='#'&&xx>=0&&yy>=0&&xx<n&&yy<n){
				tmp[xx][yy]='$';
				q.push(node{xx,yy});
			}
		}
	}
}
int main(){
	cin>>n;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			cin>>mapp[i][j];
			tmp[i][j]=mapp[i][j];
		}
	}
	int t0=0;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			if(tmp[i][j]=='#'){
				t0++;
				bfs1(i,j);
			}
		}
	}
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			if(mapp[i][j]=='#'){
				if(mapp[i+1][j]=='.'||mapp[i][j+1]=='.'||mapp[i-1][j]=='.'||mapp[i][j-1]=='.'){
					mapp[i][j]='$';
				}
			}
		}
	}
	int ans=0;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			if(mapp[i][j]=='#'){
				ans++;
				bfs(i,j);
			}
		}
	}
	if(ans>=t0){
		cout<<0;
		return 0;
	}  
	cout<<t0-ans;
	return 0;
}

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