#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#ifdef __GXX_EXPERIMENTAL_CXX0X__
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#ifdef __GXX_EXPERIMENTAL_CXX0X__
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif


using namespace std;

int main()
{
	int N;
	while (cin >> N, N)
	{
		vector<vector<bool> >data;
		data.resize(N * 2 + 2);
		for (size_t i = 0; i < N * 2 + 2; i++)
		{
			data[i].resize(N + 1);
		}
		string str;
		for (size_t i = 0; i < N; i++)
		{
			cin >> str;
			for (size_t j = 0; j < N; j++)
			{
				if (str[j] == '.')
				{
					data[i][j] = 1;
				}
			}
		}
		
		int ans = 0;
		for (size_t i = 0; i < N; i++)
		{
			for (size_t j = 0; j < N-ans; j++)
			{
				int k = ans;
				bool f = 1;
				while (f&&j + k <= N)
				{
					for (size_t l = 0; f&&l < k; l++)
					{
						for (size_t m = 0; f&&m < k; m++)
						{
							if (data[i + l][j + m] != 1)
							{
								f = 0;
							}
						}
					}
					if (f)
					{
						if (ans < k)
						{
							//cout << i << " " << j <<" "<<k<< endl;
							ans = k;
						}
						//ans = max(ans, k);
					}
					k++;
				}
			}
		}
		cout << ans << endl;
	}
}