#include <iostream>

int main()
{
	const unsigned long long f = 18446744073709551615;
	unsigned long long a = 12297829382473034410;
	std::cin >> a;

	int it = 0;
	while (a % 3 != 0)
	{
		a = a - f;
		it++;
	}

	a = a / 3 + (f / 3) * it;
	std::cout << a;
}