#include <iostream>
#include <cstdio>
#include <vector>
#include <map>
#include <queue>
#include <string>
#include <algorithm>

#define REP(i, n) for(ll i = 0; i < (n); i++)
#define INF 1e16
#define MOD 1e9 + 7

using namespace std;
using ll = long long;



int main() {
	ll n;
	cin >> n;
	vector<ll> dp(n + 2);
	dp[0] = 1;
	REP(i, n) {
		dp[i + 1] += dp[i];
		dp[i + 2] += dp[i];
	}
	cout << dp[n] << endl;
}