POJ 2407 Relatives

 1 #include<cstdio>
 2 int euler_phi(int p){
 3     int phi=p;
 4     for(int i=2;i*i<=p;i++){
 5         if(!(p%i)){
 6             phi=phi-phi/i;
 7             while(!(p%i))
 8                 p/=i;
 9         }
10     }
11     if(p>1)
12         phi=phi-phi/p;
13     return phi;
14 }
15 int main(){
16     int p;
17     while(scanf("%d",&p),p)
18         printf("%d\n",euler_phi(p));
19     return 0;
20 }