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

#define int long long
#define endl "\n"
const int N = 1e7 + 10; // 这家伙好大啊
int s[N];

// 筛法求欧拉函数值
int primes[N], cnt;
bool st[N];
int phi[N];
void euler(int n) {
    phi[1] = 1;
    for (int i = 2; i <= n; i++) {
        if (!st[i]) {
            primes[cnt++] = i;
            phi[i] = i - 1;
        }
        for (int j = 0; primes[j] * i <= n; j++) {
            st[primes[j] * i] = true;
            if (i % primes[j] == 0) {
                phi[i * primes[j]] = phi[i] * primes[j];
                break;
            }
            phi[i * primes[j]] = phi[i] * (primes[j] - 1);
        }
    }
}

signed main() {
    int n;
    cin >> n;

    // 欧拉函数筛法
    euler(n);

    // 前缀和
    for (int i = 1; i <= n; i++) s[i] = s[i - 1] + phi[i];

    int res = 0;
    for (int i = 0; i < cnt; i++)
        res += s[n / primes[i]] * 2 - 1; // 推导的公式

    cout << res << endl;
}