#include <fstream>
using namespace std;
int V[1000000], long long N, long long count;

int main()
{
   ifstream in("fractii.in");
   ofstream out("fractii.out");
   in>>N;
   in.close();
   for(i=1;i<=N;i++) V[i] = i-1;
   count=0;
   for(i=2;i<=N;i++)
   {
       for(j=(i<<1);j<=N;j+=i)
       {
          V[j]-=V[i];
       }
       count+=V[i];
    }

  count= ++(count<<1);
  out<<count<<"\n";
  out.close();
  return 0;
}