#include <bits/stdc++.h>

using namespace std;

#define INF 2000000000
#define MOD 1000000007
typedef long long ll;
typedef pair<int, int> P;


int ret = 0;
int N;
bool dfs(ll n) {
//	cout << "n: " << n << " ret: " << ret << "\n";
	if (n>N) {
		return false;
	}
	if (n==N) {
		return true;
	}

	bool a = dfs(n+1);
	bool b = dfs(n+2);
	if (a) {
		ret++;
	}
	if (b) {
		ret++;
	}
	return false;
}

int main()
{
	cin >> N;
	dfs(0);
	cout << ret << "\n";
}