#include <bits/stdc++.h>

using namespace std;

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

int main() {
    long long n;
    in >> n;

    vector<vector<long long>> nonPrimes(n + 1);
    for (long long i = 2; i <= n / 2; i++) {
        if (nonPrimes[i].empty()) {
            for (long long j = 2; j <= n / i; j++) {
                nonPrimes[i * j].push_back(i);
            }
        }
    }

    long long sol = 1;
    for (long long i = 2; i <= n; i++) {
        if (nonPrimes[i].empty()) {
            sol += (i - 1) * 2;
        } else {
            long long prod = i;
            for (const auto& p: nonPrimes[i]) {
                prod = prod * (p - 1) / p;
            }
            sol += prod * 2;
        }
    }

    out << sol;

    return 0;
}