#include <fstream>
using namespace std;

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

int prime[1000001];

int main ()
{
    int limita;
    cin >> limita;

    for (int indice = 1 ; indice <= limita ; indice++)
        prime[indice] = indice;

    for (int indice = 2 ; indice <= limita ; indice++)
        if (prime[indice] == indice)
            for (int factor = 1 ; indice * factor <= limita ; factor++)
                prime[indice * factor] = prime[indice * factor] / indice * (indice - 1);

    unsigned long long fractii = 1;
    for (int indice = 2 ; indice <= limita ; indice++)
        fractii += 2LL * prime[indice];

    cout << fractii;
    cout.close(); cin.close();
    return 0;
}