#include <iostream>
#include <algorithm>

using namespace std;

typedef long long LL;

const int N = 1e6 + 10;

int n;
int prime[N], cnt;
LL p[N];
int st[N];

void get_prime(int x) {
    p[1] = 1;

    for (int i = 2; i <= x; i++) {
        if (!st[i]) {
            prime[++cnt] = i;
            p[i] = i - 1;
        }

        for (int j = 1; prime[j] <= x / i; j++) {
            st[i * prime[j]] = 1;
            if (i % prime[j] == 0) {
                p[i * prime[j]] = p[i] * prime[j];
                break;
            }

            p[i * prime[j]] = p[i] * (prime[j] - 1);
        }
    }

    return;
}

int main() {
    cin >> n;

    get_prime(n);

    LL ans = 0;
    for (int i = 1; i < n; i++) {
        ans += p[i];
    }

    cout << (ans << 2) << endl;

    return 0;
}