#include<fstream.h>
#include<math.h>
long a[1000001],n,i,ii,j,x,y,p,m,ok;
long long nr,rad;
int main()
{
ifstream f("fractii.in");
ofstream g("fractii.out");
f>>n;
a[1]=1;
for(i=2;i<=n;i++)
 {x=i;
  p=2;
  rad=sqrt(x);
  while(p<=rad && x%p)p++;
  if(p>rad)a[i]=i-1;

  else
  {
  y=1;
  while(x%p==0){y=y*p;
		x=x/p;
		}
 y=y/p;
 a[i]=(p-1)*y*a[x];
 }

 }
 nr=1;
 for(i=2;i<=n;i++)
  nr=nr+2*a[i];
  g<<nr;
  g.close();

return 0;
}