#include <bits/stdc++.h>

int phi[1000001];

int main() {
    freopen("fractii.in", "r", stdin);
    freopen("fractii.out", "w", stdout);

    int n;
    scanf("%d", &n);
    for (int i = 2; i <= n; ++i)
        phi[i] = i;
    for (int i = 2; i <= n; ++i)
        if (phi[i] == i)
            for (int j = i; j <= n; j += i)
                phi[j] = (long long) phi[j] * (i - 1) / i;
    long long res = 1;
    for (int i = 2; i <= n; ++i)
        res += 2 * phi[i];
    printf("%lld", res);
    return 0;
}