#include <fstream>
#include <vector>

using namespace std;

int main() {
    ifstream fin("fractii.in");
    ofstream fout("fractii.out");
    int n;
    fin >> n;
    vector <int> e(n + 1);
    for (int i = 1; i <= n; i++) {
        e[i] = i;
    }
    long long suma = 1;
    for (int d = 2; d <= n; d++) {
        if (e[d] == d) {
            for (int m = d; m <= n; m += d) {
                e[m] = e[m] / d * (d - 1);
            }
        }
        suma += 2 * e[d];
    }
    fout << suma << "\n";
    fin.close();
    fout.close();
    return 0;
}