4939 欧拉函数

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 #include<algorithm>
 6 #define lli long long int 
 7 using namespace std;
 8 void read(lli &n)
 9 {
10     char c='+';lli x=0;bool flag=0;
11     while(c<'0'||c>'9')
12     {c=getchar();if(c=='-')flag=1;}
13     while(c>='0'&&c<='9')
14     {x=x*10+(c-48);c=getchar();}
15     flag==1?n=-x:n=x;
16 }
17 int main()
18 {
19     lli n;lli ans;
20     while(cin>>n)
21     {
22         if(n==0)break;
23         ans=n;
24         if(n%2==0)
25         {
26             while(n%2==0)
27                 n=n/2;
28             ans=ans/2;
29         }
30         for(lli i=3;i*i<=n;i+=2)
31         {
32             if(n%i==0)
33             {
34                 while(n%i==0)    n=n/i;
35                 ans=ans/i*(i-1);
36             }
37         }
38         if(n>1)
39             ans=ans/n*(n-1);
40         cout<<ans<<endl;
41     }
42     return 0;
43 }