#include <bits/stdc++.h>
using namespace std;

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

int phi[1000001];

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