#include<stdio.h>
#include<math.h>

typedef struct
{
  long x, e;
}  factor;

factor v[10];

long n, contor, nr, a[1000002];

void descomp(long x)
{
  int exp, d;
  d=2;
  nr=0;
  while (x!=1)
   {
     exp=0;
     if (x%d==0)
       {
	 nr++;
	 while (x%d==0)
	  {
	    exp++;
	    x/=d;
	  }
	 v[nr].e=exp;
	 v[nr].x=d;
       }
     d++;
   }
}

long totient(long x)
{
  long i, c=1;
  for (i=1; i<=nr; i++)
    c*=((v[i].x-1)*pow(v[i].x,v[i].e-1));
  return c;
}

void ciur(long x)
{
  long i;
  for (i=4; i<=x; i+=2)
    a[i]=1;
  for (i=3; i<=x; i+=2)
  {
    if (a[i]==0)
      {
	long j=i*2;
	while (j<n)
	  {
	    a[j]=1;
	    j+=i;
	  }
      }
  }
}



void citire()
{
  freopen("fractii.in","r",stdin);
  scanf("%ld",&n);
}

int main()
{
  citire();
  long i;
  contor=1;
  ciur(n);
  for (i=2; i<=n; i++)
    {
      if (a[i]==0) contor+=i-1;
	else
	 {
	   descomp(i);
	   contor+=totient(i);
	 }

    }
  freopen("fractii.out","w",stdout);
  printf("%ld",contor*2-1);
  return 0;
}