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

int main(void) {
	int n;
	cin >> n;
	vector<ll> dp(n+1);
	dp[0] = 1;
	for(int i=0;i<=n;i++){
		if(i-1>=0)dp[i] += dp[i-1];
		if(i-2>=0)dp[i] += dp[i-2];
	}
	cout << dp[n] << endl;
	return 0;
}