uva 11417 solution

#include<stdio.h>
long int GCD(long int a,long int b)
{
    if(b==0)
        return a;
    long int swap,r;
    if(a<b){
        swap=a;
        a=b;
        b=swap;
    }
    r=a%b;
    return GCD(b,r);
}
main()
{
    long int N,i,j,G;
    while(scanf("%d",&N)==1&&N!=0){
    G=0;
    for(i=1;i<N;i++){
        for(j=i+1;j<=N;j++){
            G+=GCD(i,j);
        }
    }
    printf("%d\n",G);
}
}