#include<fstream.h>
int e[1000000],n;
float pr[1000000];
long long int s=1;
long double r;


int main()
{
  int i,j;

  ifstream f("fractii.in");
  f>>n;
  f.close();

  for(i=1;i<=n;i++)
  {
    e[i]=1;
    pr[i]=1;
  }

  for(i=2;i<=n/2;i++)
   if(e[i]==1)
    for(j=2;j*i<=n;j++)
      e[i*j]=0;

  for(i=2;i<=n;i++)
  {
   if(e[i]==1)
   {
    pr[i]=i-1;
    for(j=2;j*i<=n;j++)
      {
	pr[i*j]*=i-1;
	pr[i*j]/=i;
      }
   r=pr[i];
   }
   else
     r=(long double)(pr[i]*i);
   s+=(long long int)(2*r);
  }

  ofstream g("fractii.out");
  g<<s<<"\n";
  g.close();
  return 0;
}