#include <fstream>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int n;
int phi[1000001];
int main()
{
    fin >> n ;
    long suma=1;
    ///int *phi = new int [n+1] ;
    for (int i=1; i<=n; i++) phi[i]=i;
    for (int i=2; i<=n; i++)
        if (phi[i]==i)
            for ( int j=i; j<=n; j+=i) phi[j] /=i,phi[j] *= (i-1);
    for( int i = 2 ; i <= n ; ++i )
        suma += 2*phi[i];
    fout << suma;
    return 0;
}