#include<stdio.h>int n;char map[4][4];int bestn;int canput(int row,int col){ int i; for(i=row-1;i>=0;i--) { if(map[i][col]=='X') { break; } if(map[i][col]=='o') { return 0; } } for(i=col-1;i>=0;i--) { if(map[row][i]=='X') { break; } if(map[row][i]=='o') { return 0; } } return 1;}void backtrack(int k,int current){ int x,y; if(k>=n*n) { if(current>bestn) {bestn=current; } return; } else { x=k/n; y=k%n; if(map[x][y]=='.'&&canput(x,y)) { map[x][y]='o'; backtrack(k+1,current+1); map[x][y]='.'; } backtrack(k+1,current); }} void initial(){ int i,j; for(i=0;i<4;i++) { for(j=0;j<4;j++) { map[i][j]='.'; } }}int main(){ scanf("%d",&n); while(n) { int i,j; bestn=0; initial(); for(i=0;i<n;i++) { for(j=0;j<n;j++) { char ch; ch=getchar(); if(ch=='n') { j--; continue; } else { map[i][j]=ch; } } } backtrack(0,0); printf("%dn",bestn); scanf("%d",&n); } return 0; }
