SPOJ Problem:Beehive Numbers

阅读题。。加上等差数列判断。。

#include<cstdio>
#include<cmath>
int n,s;
int main(){
    while(scanf("%d",&n)&&n!=-1){
        n--;
        if (n%6){printf("N\n");continue;}
        n/=3;
        s=int (sqrt(double(n)));
        if (s*(s+1)==n)printf("Y\n");
        else printf("N\n");
    }
}