C++ :

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long ll;
inline void read(int &x){
	x=0;char ch;bool flag = false;
	while(ch=getchar(),ch<'!');if(ch == '-') ch=getchar(),flag = true;
	while(x=10*x+ch-'0',ch=getchar(),ch>'!');if(flag) x=-x;
}
int n;
namespace work1{
	const int maxn = 2424;
	bool map[maxn][maxn];
	bool can[maxn];
char   s[maxn];
	char ch;
	int a[maxn];
	int main(){
		bool flag = false;
		for(int i=1;i<=n;++i){
		  scanf("%s",s+1);
			for(int j=1;j<=n;++j){

				map[i][j] = (s[j] == '#');
				flag |= map[i][j];
				if(map[i][j]) ++ a[j];
			}
		}
		if(!flag) return puts("-1");
		for(int i=1;i<=n;++i){
			for(int j=1;j<=n;++j){
				if(map[j][i]){
					can[i] = true;
				}
			}
		}
		int nd = 0,cost = 0,ans = 0x7f7f7f7f;
		for(int i=1;i<=n;++i){
			nd += (a[i] != n);
		}
		for(int i=1;i<=n;++i){
			cost = 0;
			bool flag = false;
			for(int j=1;j<=n;++j){
				if(map[i][j]) continue;
				++ cost;
				flag = true;
			}
			if(!can[i] && flag) ++ cost;
			ans = min(ans,cost+nd);
		}
		printf("%d\n",ans);
		return 0;
	}
}
int main(){
	read(n);
	work1::main();
//	work2::main();
	return 0;
}