#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>


using namespace std;

typedef pair<int, int> P;
typedef long long ll;

#define MAX_N 50

int N;

ll dp[MAX_N + 5];

int main() {

	cin >> N;

	dp[0] = dp[1] = 1;

	for (int i = 2; i <= N; i++){
		dp[i] = dp[i - 1] + dp[i - 2];
	}

	cout << dp[N] << endl;

	return 0;
}