#include <iostream>
#include <vector>
#include <algorithm>

using namespace std ;

/*ifstream cin ("input") ;
ofstream cout ("output") ;
*/
int main(int argc, char const *argv[])
{
	long long n ; 
	cin >> n ; 
	cout << 3LL * (((n) / 2LL) + (n - 1)/2LL * 2LL) + 3LL; 
	return 0;
}