#include <bits/stdc++.h>
#define rep(i,n) for(int i=(0);i<(n);i++)

using namespace std;

typedef long long ll;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	ll n;
	cin >> n;

	vector<ll> a(n+5, 0);
	a[0] = 1;
	rep(i, n){
		a[i+1] += a[i];
		a[i+2] += a[i]; 
	}

	cout << a[n] << endl;
}