#include <iostream>
#include <iomanip>
#include <cassert>
#include <algorithm>
#include <functional>
#include <vector>
#include <string>
#include <cstring>
#include <stack>
#include <queue>
#include <map>
#include <bitset>
#include <sstream>
#include <istream>
#include <cmath>
#include <cstdio>
#include <complex>

using namespace std;

#define vci vector<int>
#define vcs vector<string>
#define pb push_back
#define sz size()
#define mapii map<int, int>
#define mapci map<char, int>
#define mapsi map<string, int>
#define all(x) x.begin(), x.end()
#define minit(a, i) memset(a, i, sizeof(a));

#define for_(i, a, b) for (int i=(int)a; i<(int)b; i++)
#define for_d(i, a, b) for (int i=(int)a-1; i>=b; i--)
#define for_r(i, a, b, c) for (int i=(int)a; i<(int)b; i += c)
#define for_dr(i, a, b, c) for (int i=(int)a-1; i>=b; i -= c)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)

template <class T> int __builtin_popcount(T n) { return n ? 1 + __builtin_popcount(n & (n - 1)) : 0; }

typedef long long ll;
typedef double D;

const int iINF = 2147483647;
const ll lINF = 9223372036854775807;

template <class T> inline void dbg(T t) { cout << t << endl; }



int vert[1024];
int csize[2][1024];

int main() {
	int n;
	
	while (1) {
		cin >> n; if (n==0) break;
		
		int ans = 0;
		minit(vert, 0); minit(csize, 0);
		string line;
		
		for_(i, 0, n) {
			cin >> line;
			int horiz = 0;
			int *can = csize[i&1];
			int *prev = csize[(i+1)&1];
			
			for_(j, 1, n+1) {
				if (line[j-1]=='.') {
					horiz++;
					vert[j]++;
					
					can[j] = min(prev[j-1]+1, min(horiz, vert[j]));
					ans = max(ans, can[j]);
				} else {
					can[j] = vert[j] = horiz = 0;
				}
			}
		}
		
		cout << ans << endl;
	}
	
	return 0;
}