#include<fstream.h>
#include<math.h>

 ifstream f("fractii.in");
 ofstream g("fractii.out");

 long long sir[1000000],n,i,s,j;

int main()
{
 f>>n;
 i=2;
 sir[2]=1;
 while(i<=n)
 {
  if(sir[i]==0) sir[i]=i-1;
  for(j=2*i;j<=n;j+=i)
   if(sir[j]==0)
     sir[j]=(j*(i-1))/i;
   else sir[j]=(sir[j]*(i-1))/i;
  while(sir[i])i++;
 }
 for(i=1;i<=n;i++) s+=sir[i]*2;
 g<<(s+1);
 f.close();
 g.close();
 return 0;
}