#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <sstream>
#include<set>
#include<stack>

//#include<bits/stdc++.h>


using namespace std;	



int main() {

	
	int n;
	cin >> n;
	
	vector<long long int>t(n+10);
	t[0] = 1;
	for (int i = 0; i < n; i++) {
		t[i + 1] += t[i];
		t[i + 2] += t[i];
	}
	cout << t[n] << endl;


	return 0;




}