#include <iostream>
#include <fstream>

using namespace std;

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

int phi[1000100];

int main ()
{
	int N, i, j;
	long long sol = 1;
	
	in >> N;
	
	for (i = 2; i <= N; i ++)
		phi[i] = i;
	
	for (i = 2; i <= N; i ++)
		if (phi[i] == i)
			for (j = i; j <= N; j += i)
				phi[j] = (i - 1) / i * phi[i];
			
	for (i = 2; i <= N; i ++)
		sol += phi[i] << 1;
	
	out << sol;
	
	return 0;
}