#include <iostream>
#include <bits/stdc++.h>
#include <time.h>
#include <sys/timeb.h>
#include <cstdio>
#include <sys/time.h>

using namespace std;
#define ll long long
#define uint unsigned int
#define ulong unsigned long long int

template<typename T> bool InRange(T t, T l, T r){ return l <= t && t < r; }
vector<string> split(string src, char delim = ' '){
	vector<string> ret;
	int r = 0;
	int N = src.length();
	for(int l=0;l<N;l++){
		r = l;
		while(r < N && src[r] != delim) r++;
		ret.push_back(src.substr(l, r - l));
		l = r;
	}
	return ret;
}

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