#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;

int main()
{
	int n; cin>>n;
	ll dp[51];
	dp[1]=1, dp[2]=2;
	for(int i=3; i<=n; i++) dp[i]=dp[i-1]+dp[i-2];
	cout<<dp[n]<<endl;
	return 0;
}