纯dfs
#include <iostream>
#include <cstdio>
#include <iomanip>
#include <string>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
using namespace std;
char board[5][5];
int dir[4][2]= {0,1,0,-1,1,0,-1,0};
int vis[5][5];
int maxnum;
int n;
bool judge(int x,int y)
{
for(int i=0; i<4; i++)
{
int nx=x+dir[i][0];
int ny=y+dir[i][1];
while(nx>=0&&nx<n&&ny>=0&&ny<n)
{
if(board[nx][ny]=='X') break;
if(vis[nx][ny]) return true;
nx+=dir[i][0];
ny+=dir[i][1];
}
}
return false;
}
void dfs(int x,int y,int num)
{
if(num>maxnum)
maxnum=num;
for(int i=0; i<n; i++)
{
for(int j=0; j<n; j++)
{
if(!vis[i][j]&&!judge(i,j)&&board[i][j]&&board[i][j]=='.')
{
vis[i][j]=1;
dfs(i,j,num+1);
vis[i][j]=0;
}
}
}
}
int main()
{
while(~scanf("%d",&n)&&n)
{
for(int i=0; i<n; i++)
scanf("%s",board[i]);
maxnum=-1;
memset(vis,0,sizeof(vis));
dfs(0,0,0);
cout<<maxnum<<endl;
}
}