#include <bits/stdc++.h>

using namespace std;

const int Nmax = 1e6 + 10;

int n , i , j;
int phi[Nmax];

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

    scanf("%d", &n);

    for (i = 1; i <= n; ++i)
        phi[i] = i;

    for (i = 2; i <= n; ++i)
        if (phi[i] == i)
            for (j = i; j <= n; j += i) phi[j] = phi[j] / i * (i - 1);

    long long sum = 0LL;
    for (i = 1; i <= n; ++i) sum += phi[i];
    sum <<= 1LL; sum--;
    printf("%lld\n", sum);

    return 0;
}