SGU 102

For given integer N (1<=N<=10⁴) find amount of positive numbers not greater than N that coprime with N. Let us call two positive integers (say, A and B, for example) coprime if (and only if) their greatest common divisor is 1. (i.e. A and B are coprime iff gcd(A,B) = 1).

Input

Input file contains integer N.

Output

Write answer in output file.

Sample Input

9

Sample Output

6

首先找出n的质因子，然后走一次o(n)找出所有不互质的数，减去即可，注意1与自身互质。

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 using namespace std;

 #define maxn 10005

 int n,len = ;
 int ele[];
 bool prime[maxn],vis[maxn];

 void solve() {
     for(int i = ; i <= n; i++) {
             prime[i] = i % ;
     }

     prime[] = ;
     int ans = n;
     for(int i = ; i < n; i++) {
             if(prime[i]) {
                     if(n % i == ) {
                             ele[len++] = i;
                     }
                     for(int j = i; j * i <= n; j++) {
                             prime[j * i] = ;
                     }

             }
     }

     vis[] = ;
     int sum = ;
     for(int i = ; i < len; i++) {
             for(int j = ; j < n; j++) {

                     if(j % ele[i] == ) vis[j] = ;
             }
     }

     for(int j = ; j < n; j++) if(vis[j]) sum++;
     sum++;
     if(prime[n]) printf("%d\n",n - );
     else
     printf("%d\n",ans - sum);

 }
 int main()
 {

     scanf("%d",&n);

     if(n == ) printf("1\n");
     else solve();

     //cout << "Hello world!" << endl;
     return ;
 }