#include <stdio.h>

char sir[1000001];
int t[1000001];

int main ()
{
  long double nrfractii;
  int i ,j, q, n;

  freopen("fractii.in", "r", stdin);
  freopen("fractii.out", "w", stdout);
  scanf("%d", &n);
  
  nrfractii=1;
  t[1]=1;

  for(i=2;i<=n;i++)
  {
    if(sir[i]==0)
    {
      t[i]=i-1;
	  if(i<=n/i+1)
	  	for(j=i*i; j<=n; j*=i)
			t[j]=t[j/i]*i;
	  
	  for(j=i*2; j<=n; j+=i)
	  {
			sir[j]=1;
			for(q=i; q<=n && j%q==0; q*=i)
				if(!t[j] && (j/i)%q!=0)
					t[j]=t[q]*t[j/q];			  	  
	  }	  	  
	}
	nrfractii+=2*t[i];
  }
  printf("%.Lf", nrfractii);
  return 0;
}