#include <iostream>
using namespace std;

int main()
{
	int n;
	cout << "\n n = ?";
	cin >> n;

	int a[n + 1];
	a[0] = 0;
	a[1] = 1;

	if (n >= 2)
	{
		for (int i = 2; i <= n; i++)
		{
			a[i] = 2 * a[i - 1] + 3 * a[i - 2];
		}
	}

	cout << " => a(" << n << ") = " << a[n] << endl << endl;

	system("pause");
}