hdu 1787 GCD Again

简单的欧拉函数……

#include<iostream>
using namespace std;
typedef __int64 int64;
//const long mod=1000000007;
int64 fun(int64 n)
{
    int64 ans=1;
    for(int i=2;i*i<=n;i++)
    {
        if(n%i==0)
        {
            n/=i;
            ans=ans*(i-1);
            while(n%i==0)
            {
                n/=i;
                ans=ans*i; } } }
    if(n>1)
        ans*=n-1;
    return ans;
}
int main()
{
    int64 n,sum;
    while(scanf("%I64d",&n),n)
    {
        sum=n-fun(n)-1;
        printf("%I64d\n",sum);
    }
    return 0;
}