hdu1787GCD Again

 1 #include <iostream>   

 2 using namespace std;  

 3 //  x=p1^e1*p2^e2~~~pn^en 

 4 //phi(x)=(p1-1)*p1^(e1-1)*(p2-1)*p2^(e2-1)~~~(pn-1)*pn^(en-1)

 5 int phi(int m)  

 6 {  

 7     int i,s=1;  

 8     for(i=2;i*i<=m;i++)  {  

 9         if(m%i==0){  

10             m/=i;  

11             s*=i-1;  

12             while(m%i==0) {  

13                 m/=i;  

14                 s*=i;  

15             }  

16         }  

17     }  

18     if(m>1)  

19         s*=m-1;  

20     return s;  

21 }  

22 int main()  

23 {  

24     int m;  

25     while(cin>>m && m)

26         cout<<m-1-phi(m)<<endl;  

27     return 0;  

28 }