#include <fstream>
#include <queue>
#include <vector>

using namespace std;

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

int n;
long long rez = 1;

int f(int n)
{
     int i = 1, rez = n;

     if(n % 2 == 0)
     {
         rez /= 2;
     }
     while(n % 2 == 0)
     {
         n /= 2;
     }

     while(n > 1)
     {
         i += 2;

         if(n % i == 0)
         {
             rez *= (i - 1);
             rez /= i;
         }
         while(n % i == 0)
         {
             n /= i;
         }
     }

     return rez;
}


int main()
{
    fin >> n;

    for(int i = 2; i <= n; i++)
    {
        rez += 2 * f(i);
    }

    fout << rez;


    return 0;
}