#include <iostream>

using namespace std;

int N, NFractii[1000005], S;

int main()
{
    freopen ("fractii.in", "r", stdin);
    freopen ("fractii.out", "w", stdout);
    scanf ("%d", &N);
    for (int i=1; i<=N; ++i)
    {
        NFractii[i]=i;
        S+=i;
    }
    for (int i=1; i<=N; ++i)
    {
        for (int j=2*i; j<=N; j+=i)
        {
            NFractii[j]--;
            S--;
        }
    }
    printf ("%d\n", 2*S-1);
    return 0;
}