#include <iostream>
using namespace std;

typedef long long ll;

ll conbi(ll a, ll b)
{
	if (b == 0)
		return 1;
	return a * conbi(a - 1, b - 1) / b;
}

int main()
{
	ll N;
	cin >> N;

	ll ans = 0;
	for (ll i = 0; i <= N / 2; ++i)
		ans += conbi(N - i, i);

	cout << ans << endl;

	return 0;
}