#include <stdio.h>
#include <malloc.h>
unsigned long n;
double* totient;


double calcul(int n)
{
         int i,j;
         double s=0;
         totient[2]=1;
         for(i=2; i<=n/2; i++)
         {
              if (totient[i]==0) totient[i]=1;
              if (totient[i]==1)
              {     
                   for (j=i+i; j<=n; j+=i)
                   {
                       if (totient[j]==0) totient[j]=1;
                       if (totient[j]>1) totient[j]=totient[j]*(i-1)/i;
                       else totient[j]=j*(i-1)/i;
                   }
              }
              if (totient[i]==1) totient[i]=i-1;
              s+=totient[i];
         } 
         for (i=n; i>n/2; i--)   
         {
             if ((totient[i]==0) || (totient[i]==1)) totient[i]=i-1;
             s+=totient[i];
         }
         return s;
}


int main()
{
    FILE *f, *g;
    f=fopen("fractii.in","r");
    fscanf(f,"%lu",&n);
    totient=(double*) calloc ((n+1),sizeof(double));
    g=fopen("fractii.out","w");
    fprintf(g,"%lf",2*calcul(n)+1);
    return 0;
}