#include <fstream>

using namespace std;

ifstream in("cicada.in");
ofstream out("cicada.out");

int cmmdc(int a,int b){
    int r;
    while(b)
    {
            r=a%b;
            a=b;
            b=r;
    }

   return a;}
   int euler(int n)
   {
       int e=n,d=2;
       while(d*d<=n)
        {
           if(n%d==0)
           {
              while(n%d==0)
              {
                  n/=d;
              }
              e=e/d*(d-1);
           }
           d++;
        }
        if(n!=1)
        {
            e=e/n*(n-1);
        }
        return e;


   }
int main()
{
    int n;
    in>>n;
    out<<(long long)n*(n-1)-n-(long long)n*euler(n)/2;

    return 0;
}