#include <stdio.h>
#include <stdlib.h>
int e[1000000];
int main()
{
  int i,j,n;
  long long rez=1;
  FILE*fin,*fout;
  fin=fopen("fractii.in","r");
  fscanf(fin,"%d", &n);
  fclose(fin);
  for(i=2;i<=n;i++)
    e[i]=i;
  for(i=2;i<=n;i++)
    if(e[i]==i)
      for(j=i;j<=n;j+=i)
        e[j]=e[j]/i*(i-1);
  for(i=1;i<=n;i++)
    rez=rez+2*e[i];
  fout=fopen("fractii.out","w");
  fprintf(fout,"%lld", rez);
  fclose(fout);
  return 0;
}