#include <bits/stdc++.h>
using namespace std;

int64_t dp[51];

int64_t recursive(int n) {
	if(n == 0) return 1;
	if(n < 0) return 0;
	if(dp[n] >= 0) return dp[n];
	dp[n] = recursive(n - 1) + recursive(n - 2);
	return dp[n];
}

int main() {
	int64_t N;
	cin >> N;
	for(int i = 0; i <= 50; i++) dp[i] = -1;
	cout << recursive(N) << endl;
	return 0;
}