#include<map>
#include<set>
#include<list>
#include<cmath>
#include<queue>
#include<stack>
#include<cstdio>
#include<string>
#include<vector>
#include<complex>
#include<cstdlib>
#include<cstring>
#include<numeric>
#include<sstream>
#include<iostream>
#include<algorithm>
#include<functional>

#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,b,n) for(int i=b;i<n;i++)

using namespace std;

typedef    long long          ll;
typedef    unsigned long long ull;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      pii;

const int INF=1<<29;
const double EPS=1e-9;

const int dx[]={1,0,-1,0},dy[]={0,-1,0,1};
char board[1100][1100];
int main(){
	int n;
	while(cin>>n,n){
		rep(i,1100)rep(j,1100)board[i][j]='\0';
		bool fi =false;
		rep(i,n){
			rep(j,n){
				cin>>board[i][j];
				if(board[i][j]=='.'){
					fi =true;
				}
			}
		}
		if(!fi){
			cout <<0<<endl;
			continue;
		}
		bool suc =false;
		for(int s =n; s>=1&&!suc;s--){//正方形のs*s
			for(int i =0;i <n&&!suc;i++){//正方形の左上
				for(int j =0;j <n&&!suc;j++){
					if(board[i][j]=='.'&&i+s-1<n&&j+s-1<n){
						bool flag =true;
						for(int y =0;y <=s-1&&flag;y++){
							for(int x =0;x <=s-1&&flag;x++){
								int ty =i +y;
								int tx =j + x;
								if(board[ty][tx]=='*'){
									flag =false;
									j +=x;
									break;
								}
							}
						}
						if(flag){
							suc =true;
							cout <<s<<endl;
						}
					}
				}
			}
		}
		if(!suc){
			cout <<0<<endl;
		}

	}
	return 0;
}