#include<iostream>
using namespace std;

int main()
{
	int n;
	unsigned long long a[71];
	a[0] = a[1] = 1;
	a[2] = 2;
	a[3] = 4;
	for (int i = 4; i <= 70; i++)
	{
		a[i] = 2 * a[i - 1] - a[i - 4];
	}
	while (cin >> n)
	{
		cout << a[n] << endl;
	}
	return 0;
}