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

int main(){
    int N;
    cin >> N;
    int sqrt_N = sqrt(N);

    // 線形篩で前計算 Θ(√N)時間
    vector<int> primes, least_prime_factor(sqrt_N + 1);
    for(int i = 2; i <= sqrt_N; ++i){
        if(!least_prime_factor[i]){
            primes.emplace_back(i);
            least_prime_factor[i] = i;
        }
        for(const auto p : primes){
            if(p * i > sqrt_N || p > least_prime_factor[i])break;
            least_prime_factor[p * i] = p;
        }
    }

    // φ(2), φ(3), ..., φ(Floor(√N)) を線形篩を用いて計算 Θ(√N)時間
    vector<int> totient(sqrt_N + 1);
    for(int i = 2; i <= sqrt_N; ++i){
        const auto p = least_prime_factor[i];
        totient[i] = i == p ? i - 1
                   : least_prime_factor[i / p] == p ? p * totient[i / p]
                   : (p - 1) * totient[i / p];
    }

    // 答えは 2 * ∑ Floor(N/i²) φ(i) + N
    int ans = 0;
    for(int i = 2; i <= sqrt_N; ++i)ans += N / i / i * totient[i];
    cout << 2 * ans + N << endl;

    return 0;
}