#include<iostream>
#include<fstream>
#include<math.h>
using namespace std;

int prime(int x)
{
	int stop = sqrt(x),i;
	for(i=2;i<=stop;i++)
		if(x%i==0)
			return 0;
	return 1;
}

int main ()
{
	int n;
	cin>>n;
	if(n==2) 
		cout<<"1";
	else if(n==3)
		cout<<"2";
	else if(n==4)
		cout<<"2";
	else {
		if(prime(n))
			cout<<n-1;
		else cout<<"0";
	}
	return 0;
}