#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int n, phi[1000001];
int main()
{
    f >> n;
    long sol=1;
    for(int i=2;i<=n;i++) phi[i] = i-1;
    for(int i=2;i<=n;i++)
    {
        for(int j=(i<<1);j<=n;j+=i) phi[j]-=phi[i];
        sol+=2*phi[i];
    }
    g << sol << endl;
    return 0;

}