ACM step 1.2.3 hide handkerchief

The Children’s Day has passed for some days .Has you remembered something happened at your childhood? I remembered I often played a game called hide handkerchief with my friends.
Now I introduce the game to you. Suppose there are N people played the game ,who sit on the ground forming a circle ,everyone owns a box behind them .Also there is a beautiful handkerchief hid in a box which is one of the boxes .
Then Haha(a friend of mine) is called to find the handkerchief. But he has a strange habit. Each time he will search the next box which is separated by M-1 boxes from the current box. For example, there are three boxes named A,B,C, and now Haha is at place of A. now he decide the M if equal to 2, so he will search A first, then he will search the C box, for C is separated by 2-1 = 1 box B from the current box A . Then he will search the box B ,then he will search the box A.
So after three times he establishes that he can find the beautiful handkerchief. Now I will give you N and M, can you tell me that Haha is able to find the handkerchief or not. If he can, you should tell me "YES", else tell me "POOR Haha".

求最大公约数的一道题，如果m,n不互质的话就会有一些同学永远不会被点到。

//

// main.c

// hdu1.2.3

//

// Created by wuxi on 14-10-27.

// Copyright (c) 2014年 wuxi. All rights reserved.

//

#include <stdio.h>

int gcd(int x,int y)

{

if (x%y==0) return y;

return gcd(y,x%y);

}

int main() {

int m,n,q;

while(1){

scanf("%d%d",&m,&n);

if (m==-1 && n==-1) break;

if (m>=n )

q=gcd(m,n);

else q=gcd(n,m);

if (q==1) printf("YES\n");

else printf("POOR Haha\n");

}

return 0;

}