#include<fstream.h>

int main()
{
	ifstream fin("fractii.in");
	ofstream fout("fractii.out");
	long n,s=0;
	fin>>n;
	if (n==1)
	{
	fout<<1;
	fin.close();
	fout.close();
	return 0;
	}
	if (n==2)
	{
	fout<<2;
	fin.close();
	fout.close();
	return 0;
	}
	
	if (n%2==1)
	s=7+12*(n/2-1);
	else
	if (n%2==0)
	s=11+12*(n/2-2);
	
	fout<<s;
	fin.close();
	fout.close();
	return 0;
	
}


/*3 7
4 11
5 19
6 23
7 31
8 35
*/