#include <iostream>
#include <fstream>

using namespace std;

ifstream in("fractii.in");
ofstream out("fractii.out");

const int maxn = 1000005;

int n;
long long int rez = 1;
int a[maxn];

int main(){
	in >> n;
	for(int i = 2; i <= n; ++i)
		a[i] = i;
	for(int i = 2; i <= n; ++i){
		if(a[i] == i)
			for(int j = i; j <= n; j+=i)
				a[j] = a[j] / i * (i - 1);
		rez += a[i] * 2;
	}	
	out << rez;
	return 0;
}