#include <iostream.h>
#include <fstream.h>

#define NMAX 10000
#define NMAX_ 10000

int main(void)
{
 fstream f1("sarpe.in",ios::in);
 fstream f2("sarpe.out",ios::out);
 long long N = 0;
 long long N_ = 0;
 long long a = 0;
 f1 >> N;
 for (a = (N / 2);a <= (N - 2);a = a + 1)
  {
   N_ = N_ + a;
  }
 N_ = N_ + N;
 if (N > 3)
   {
    N_ = N_ + ((N / 2) - 1);
   }
 N_ = N_ - (N % 2);
 N_ = N_ * 4;
 f2 << N_;
 f1.close();
 f2.close();
 return 0;
}