C++ :

#include<stdio.h>
#define I int
I n,f,a=1<<20,h[1005],l[1005],t,i,j,F;
char s[1005];
I m(I a,I b){return a>b?b:a;}
I main(){
	scanf("%d",&n);
	for(i=1;i<=n;i++,t+=F,F=0){
		scanf("%s",s+1);
		for(j=1;j<=n;j++)
		if(s[j]=='#')f=l[j]=1,++h[i];
		else F=1;
	}
	if(!f)return puts("-1"),0;
	for(i=1;i<=n;i++) a=m(a,n+t-h[i]+!l[i]);
	printf("%d",a);
}