#include<cstdio>
#include <iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

#define mod 1000000007;

using namespace std;
typedef long long ll;
typedef pair<ll, ll> Pr;


ll memo[52];

int main()
{
	int N;
	cin >> N;

	memo[0] = 1;
	memo[1] = 1;
	for (int i = 1; i < N; i++) {
		memo[i + 1] = (memo[i] + memo[i - 1]);
	}
	cout << memo[N] << endl;
	return	0;
}