#include<fstream.h>
unsigned long long  n,i,j,p,v[1000001],sol=1;
int main()
{ifstream q("fractii.in");
ofstream w("fractii.out");
q>>n;
for(i=2;i<=n;i++)
  {if(!v[i])
    {v[i]=i-1;
    for(j=i*i;j<=n;j=j+i)
      v[j]=i;}
   else
    {p=v[i];
    j=i;
    v[i]=p-1;
    j=j/p;
    while(j%p==0)
      {v[i]=v[i]*p;
      j=j/p;}
    if(j>1)
     v[i]=v[i]*v[j];}
  sol=sol+2*v[i];}
w<<sol;
return 0;
}