C++ :

#include<stdio.h>
#include<string.h>
char a[6][6];
int b[6][6];  
int all;
int n;
int max(int as,int ad)
{
	if (as>ad) return as;
	else return ad;
}
int min(int as,int ad)
{
	if (as<ad) return as;
	else return ad;
}
int  check(int x,int y)
{
	int xx=1;
	for (int i=x;i<(min(n,x+2));i++)
	{
		if (b[i][y]==2&&i!=x) break;
		if (b[i][y]==1||b[x][y]==2) {xx=0;break;}
	}
	for (int i=x;i>=max(x-2,0);i--)
	{
		if (b[i][y]==2) break;
		if (b[i][y]==1) {xx=0;break;}
	}
	for (int i=y;i<min(y+2,n);i++)
	{
		if (b[x][i]==2&&i!=y) break;
		if (b[x][i]==1||b[x][y]==2) {xx=0;break;}
	}
	for (int i=y;i>=max(y-2,0);i--)
	{
		if (b[x][i]==2) break;
		if (b[x][i]==1) {xx=0;break;}
	}
	return xx;
}


void dfs(int kk,int x,int y)
{
	if (kk>all) all=kk;
	for (int i=y+1;i<n;i++)
	{
		//printf("(%d,%d)=%d\n",x,i,b[x][i]);
		if (check(x,i))
				{
					
					b[x][i]=1;
					dfs(kk+1,x,i);
					b[x][i]=0;
				}
	}
	for (int i=x+1;i<n;i++)
		{
			for (int j=0;j<n;j++)
			{
				//printf("(%d,%d)=%d\n",i,j,b[i][j]);
				if (check(i,j))
				{
					
					b[i][j]=1;
					dfs(kk+1,i,j);
					b[i][j]=0;
				}
			}
		}
}
int main()
{
	while(scanf("%d",&n)!=EOF&&n!=0)
	{
		getchar();
		memset(b,0,sizeof(b));
		for (int i=0;i<n;i++)
		{
			for (int j=0;j<n;j++)
			{
				scanf("%c",&a[i][j]);
				if (a[i][j]=='X') b[i][j]=2;
			}
			getchar();
		}
		all=0;
		for (int i=0;i<n;i++)
		{
			for (int j=0;j<n;j++)
			{
				if (check(i,j))
				{
				
					b[i][j]=1;
					int sum=1;
					dfs(sum,i,j);
					b[i][j]=0;
				}
			}
		}
		printf("%d\n",all);
	}
	return 0;
}