#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <vector>
#include <queue>
#include <utility>
using namespace std;

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

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define Rep(i, n) For(i, 0, (n))

const int inf = 999999999;
const int mod = 1000000007;

ll dp[60];

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