#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000

int main(){
	
	long long n;
	cin>>n;
	
	vector<long long> dp(n+1,0);
	dp[0] = 1;
	
	rep(i,n){
		dp[i+1] += dp[i];
		if(i!=n-1)dp[i+2] += dp[i];
	}
	cout<<dp.back()<<endl;
	
	return 0;
}