Problem:
Score : 1300 points

Problem Statement

There is a square-shaped grid with N vertical rows and N horizontal columns.
We will denote the square at the i-th row from the top and the j-th column from the left as (i,\ j).

Initially, each square is either white or black.
The initial color of the grid is given to you as characters a_{ij}, arranged in a square shape.
If the square (i,\ j) is white, a_{ij} is .. If it is black, a_{ij} is #.

You are developing a robot that repaints the grid.
It can repeatedly perform the following operation:

Select two integers i, j (1 ≤ i,\ j ≤ N). Memorize the colors of the squares (i,\ 1), (i,\ 2), ..., (i,\ N) as c_1, c_2, ..., c_N, respectively. Then, repaint the squares (1,\ j), (2,\ j), ..., (N,\ j) with the colors c_1, c_2, ..., c_N, respectively.

Your objective is to turn all the squares black.
Determine whether it is possible, and find the minimum necessary number of operations to achieve it if the answer is positive.

Constraints

2 ≤ N ≤ 500

a_{ij} is either . or #.

Partial Score

In a test set worth 300 points, N ≤ 3.

Input

The input is given from Standard Input in the following format:

N
a_{11}...a_{1N}
:
a_{N1}...a_{NN}

Output

If it is possible to turn all the squares black, print the minimum necessary number of operations to achieve the objective.
If it is impossible, print -1 instead.

Sample Input 1

2
#.
.#

Sample Output 1

3

For example, perform the operation as follows:

Select i = 1, j = 2.

Select i = 1, j = 1.

Select i = 1, j = 2.

The transition of the colors of the squares is shown in the figure below:

Sample Input 2

2
..
..

Sample Output 2

-1

Sample Input 3

2
##
##

Sample Output 3

0

Sample Input 4

3
.#.
###
.#.

Sample Output 4

2

Sample Input 5

3
...
.#.
...

Sample Output 5

5

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		// small 
		if(N>3){
			Console.WriteLine(-1);
			return;
		}
		
		int Inf = (int)1e9;
		int NN = (1<<(N*N));
		int[] dp = new int[NN];
		for(int i=0;i<NN;i++) dp[i] = Inf;
		
		int strt = 0;
		for(int i=0;i<N;i++){
			for(int j=0;j<N;j++){
				if(S[i][j] == '#'){
					strt |= (1<<(i*N+j));
				}
			}
		}
		dp[strt] = 0;
		Queue<int> Q = new Queue<int>();
		Q.Enqueue(strt);
		while(Q.Count>0){
			var now = Q.Dequeue();
			int[,] mp = new int[N,N];
			for(int i=0;i<N*N;i++){
				if(((now>>i)&1) == 1){
					mp[i/N,i%N] = 1;
				}
			}
			for(int i=0;i<N;i++){
				for(int j=0;j<N;j++){
					int[] t = new int[N];
					for(int k=0;k<N;k++){
						t[k] = mp[i,k];
					}
					int[,] nm = new int[N,N];
					for(int ii=0;ii<N;ii++){
						for(int jj=0;jj<N;jj++){
							nm[ii,jj] = mp[ii,jj];
						}
					}
					for(int k=0;k<N;k++){
						nm[k,j] = t[k];
					}
					int ns = 0;
					for(int ii=0;ii<N;ii++){
						for(int jj=0;jj<N;jj++){
							if(nm[ii,jj] == 1){
								ns |= (1<<(ii*N+jj));
							}
						}
					}
					if(dp[ns] == Inf){
						dp[ns] = dp[now] + 1;
						Q.Enqueue(ns);
					}
				}
			}
		}
		Console.WriteLine(dp[NN-1] == Inf ? -1 : dp[NN-1]);
		
		
		
	}
	int N;
	String[] S;
	public Sol(){
		N = ri();
		S = new String[N];
		for(int i=0;i<N;i++){
			S[i] = rs();
		}
	}

	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(char sep=' '){return Console.ReadLine().Split(sep);}
	static int[] ria(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>int.Parse(e));}
	static long[] rla(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>long.Parse(e));}
	static double[] rda(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>double.Parse(e));}
}