#include <iostream>

int main()
{
	long N; std::cin >> N;
	long dp[60];
	dp[1] = 1;
	dp[2] = 2;
	dp[3] = 3;

	for(long i=4 ; i<=N ; i++)
	{
		dp[i] = dp[i-2]*2 + dp[i-3];
	}
	std::cout << dp[N] << std::endl;

	return 0;
}