#include <iostream>
#include <algorithm>

using namespace std;

void solve() {
	long long n;
	cin >> n;

	if (n&1) {
		cout << (n+1)/2 * 3 + (n-1)/2 * 3 * 2;
	} else {
		cout << (n/2 + 1) * 3 + (n/2 - 1) * 3 * 2;
	}
	cout << "\n";
}

int main() {
	int tests = 1;

	for (;tests; --tests) {
		solve();
	}
}