#include<cstdio>
using namespace std;
const int NMAX = 1000000;
int ciur[NMAX + 5];

void ComputeSieve() {
    for (int i = 1; i <= NMAX; i++) {
        ciur[i] = i;
    }

    for (int i = 2; i <= NMAX; i++) {
        if (ciur[i] == i) {
            for (int j = i; j <= NMAX; j += i) {
                ciur[j] = ciur[j] / i * (i - 1);
            }
        }
    }
}

int main() {
    freopen("fractii.in", "r", stdin);
    freopen("fractii.out", "w", stdout);
    int n;
    scanf("%d",&n);
    ComputeSieve();

    long long int raspuns = 0;
    for (int i = 1; i <= n; i++) {
        raspuns += 2 * ciur[i];
    }
    printf("%lld", raspuns - 1);
    return 0;
}