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

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }

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

	int n;
	cin >> n;

	ll dp[n+1];
	rep(i, n+1) dp[i] = 0;
	dp[0] = 1;
	for(int i = 0; i <= n; i++){
		if(i+1 <= n) dp[i+1] += dp[i];
		if(i+2 <= n) dp[i+2] += dp[i]; 
	}

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