#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;
typedef pair<int, int> pii;
typedef vector<int> vi;
#define rep(i,x) for(int i=0;i<(int)(x);i++)

bool dp[51] = { false };
int n;
long long int m[51] = { 0 };

long long int search(int i){
	if (i>n) return 0;
	if (i==n) return 1;
	if (dp[i]) return m[i];
	m[i] = search(i+1) + search(i+2);
	dp[i] = true;
	return m[i];
}

int main(){
	cin >> n;
	cout << search(0) << endl;
	return 0;
}