#include <fstream>

#define N_MAX 1000001

using namespace std;

int main() {
	ifstream in("fractii.in");
	ofstream out("fractii.out");
	int n, output = 1, v[N_MAX];
	in >> n;
	int i, j;
	for(i = 2; i <= n; i++) v[i] = i-1;
	for(i = 2; i <= n; i++)
	{
		if(v[i] == i-1)
		{
			for(j = 2*i; j <= n; j += i) v[j] -= (j/i)-1;
		}
	}


	for(i = 2; i <= n; i++)
	{
		output += 2*v[i];
	}

	out << output;
}