#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("fractii.in");
ofstream fout("fractii.out");

int N;
int V[1000006];

int main()
{
    fin>>N;
    long long s=-1;
    for(int i=1;i<=N;i++)
    {
        V[i] = i;
    }

    for(int i=2;i<=N;i++)
    {
        if (V[i] == i)
        {
            for(int j=i;j<=N;j+=i)
                V[j] = V[j] - V[j]/i;
        }
    }

    for(int i=1;i<=N;i++)
        s = s + 2*V[i];

    fout<<s;

    return 0;
}