HOJ ( acm.hdu.edu.cn ) 1014

#include <stdio.h>
int main() {
   unsigned long long sum,sumX;
   int step,mod,seed;
   while (EOF!=scanf("%d%d",&step,&mod)) {
       sum=sumX=0; seed=0;
       for (int i=0;i<mod;++i) {
           sumX+=i; sum +=seed; seed=(seed+step)%mod;
       }
       printf("%10d%10d    %s Choice\n\n",step,mod,(sum==sumX?"Good":"Bad"));
   }
   return 0;
}