#include <fstream>

using namespace std;

int indicator (int n)
{
    int d = 2 , ind = n ;

    while(n != 1)
    {
        if(n % d == 0)
        {
            ind = ind * (d - 1) / d ;
            while(n % d == 0)
                n = n / d ;
        }

        d++;
    }

    return ind ;
}

long long sum ;

int main()
{
    FILE *fin , *fout ;
    fin = fopen("fractii.in" , "r") ;
    fout = fopen("fractii.out" , "w") ;

    int n ;
    fscanf(fin , "%d" , &n) ;

    sum++;
    for(int i = 2 ; i <= n ; i++)
        sum = sum + indicator(i) * 2 ;

    fprintf(fout , "%lld" , sum) ;
    fclose(fin) ;
    fclose(fout) ;
    return 0;
}