C++ :

#include<cstdio>
#include<iostream>
#include<cmath>
using namespace std;
long long len=0,n;
double ans,a[100000]={0};
bool judge(long long x)
{
	for(int i=2;i<=sqrt(x);i++)
	if(x%i==0) return 0;
	return 1;
}
int main()
{
	scanf("%d",&n);
	if(!n) 
	{
		cout<<0;
		return 0;
	}
	ans=n;
	if(judge(n)) 
	{
		ans-=1;
		cout<<(long long)ans;
		return 0;
	}
	long long j=2;
	while(n!=1)
	{
		if(!(n%j)) 
		{
			n/=j;
			if(a[len]!=j) a[++len]=j;
			if(judge(n)) 
			{
				if(n!=j) a[++len]=n;
				break;
			}
		}
		else j++;
	}
	for(int i=1;i<=len;i++) ans*=(1-1/a[i]);
	cout<<(long long)ans;
	return 0;
}