#include<fstream.h>

long int n;

int main()
{ 
    long int sum;
   sum=0;
  ifstream f("fractii.in");
   f>>n;   
   f.close();
  ofstream g("fractii.out");
  if(n==1) g<<1;
  if(n==2) g<<3;
  if(n==3) g<<n+2;
  if(n>3) {
           if(n%2==0) g<<n+(n/2)*2+(n/2-1)*2;
             else     if(n%2!=0) g<<n+(n/2-1)*2+(n/2-1)*2;
                   
            }        
    return 0;
}