#include <bits/stdc++.h>
using namespace std;

using ll = long long;
#define rep(i, n) for(int i = 0; i < n; i++)

int main() {
	int N;
	cin >> N;
	vector<ll> dp(N + 1);
	dp[0] = 1;
	rep(i, N) {
		dp[i + 1] += dp[i];
		if(i + 2 < N + 1) dp[i + 2] += dp[i];
	}
	cout << dp[N] << endl;
}