#include<fstream.h>
#include<alloc.h>

int main()
{
  long n,i,j;
  long *x;
  double s=0;
  ifstream f("fractii.in");ofstream g("fractii.out");
  f>>n;
  x=(long*)malloc(n*sizeof(long));
  for(i=1;i<=n;i++)x[i]=i;
  for(i=2;i<=n;i++)
    if(x[i]==i)
      for(j=i;j<=n;j+=i){x[j]/=i;x[j]*=(i-1);}
  for(i=2;i<=n;i++)s+=x[i];
  s*=2;s++;
  g.setf(ios::fixed);g<<s;
  f.close();g.close();
  return 0;
}