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

using ll=long long;
ll mod=1000000007;
ll INF=1LL<<60;

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