#include <iostream>
#include <map>
#include <set>
#include <algorithm>
#include <vector>
#include <string>
#include <string.h>
using namespace std;

int main()
{
	ios::sync_with_stdio(false);

	long long n; cin >> n;
	long long res;


	n -= 1LL;
	if (n % 2 == 1) {
		long long six = n / 2LL;
		long long three = n / 2LL + 1LL;

		res = 3LL + six * 6LL + 3LL * three;
		cout << res;
	}
	else {
		long long six = n / 2LL;
		long long three = n / 2LL;

		res = 3LL + six * 6LL + 3LL * three;
		cout << res;
	}


	return 0;
}