【SGU 102】Coprimes

102. Coprimes

time limit per test: 0.5 sec.
memory limit per test: 4096 KB

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

　　 题目让求小于N且与N互质的数的个数。因为看范围貌似暴力就可以，所以我就写了欧拉函数（= =!）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
using namespace std;

int n;

int phi(int x){
	int ans=x;
	for(int i=2;i<(int)sqrt(x*1.0)+1;i++)
		if((x%i==0)){
			ans=ans/i*(i-1);
			while((x%i==0)) x/=i;
		}
	if(x>1) ans=ans/x*(x-1);
	return ans;
}

int main(){
	scanf("%d",&n);
	printf("%d\n",phi(n));
	return 0;
}