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 = 0;
int ele[20];
bool prime[maxn],vis[maxn];

void solve() {
    for(int i = 3; i <= n; i++) {
            prime[i] = i % 2;
    }

    prime[2] = 1;
    int ans = n;
    for(int i = 2; i < n; i++) {
            if(prime[i]) {
                    if(n % i == 0) {
                            ele[len++] = i;
                    }
                    for(int j = i; j * i <= n; j++) {
                            prime[j * i] = 0;
                    }

            }
    }

    vis[1] = 1;
    int sum = 0;
    for(int i = 0; i < len; i++) {
            for(int j = 2; j < n; j++) {

                    if(j % ele[i] == 0) vis[j] = 1;
            }
    }

    for(int j = 2; j < n; j++) if(vis[j]) sum++;
    sum++;
    if(prime[n]) printf("%d
",n - 1);
    else
    printf("%d
",ans - sum);

}
int main()
{

    scanf("%d",&n);
    
    if(n == 1) printf("1
");
    else solve();


    //cout << "Hello world!" << endl;
    return 0;
}