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

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

int main() {
    int n; 
    fin >> n;
    long long ciur[n + 1];

    for (int i = 1; i <= n; ++i) {
        ciur[i] = i;
    }

    for (int i = 2; i <= n; ++i) {
        if (ciur[i] == i) {
            for (int j = i; j <= n; j += i) {
                ciur[j] = ciur[j] * (i - 1) / i;
            }
        }
    }

    long long nr = 1;

    for (int i = 2; i <= n; ++i) {
        nr += 2 * ciur[i];
    }

    fout << nr;

    fin.close();
    fout.close();

    return 0;
}