#include<bits/stdc++.h>
#include <atcoder/all>
#ifdef LOCAL
#include <debug_print.hpp>
#define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (static_cast<void>(0))
#endif
using namespace atcoder;
using mint=modint1000000007;
using namespace std;
using ll=long long;
using ul=unsigned long long;
int dx[9] = {-1, 1, 0, 0, -1, -1, 1, 1, 0};
int dy[9] = {0, 0, -1, 1, -1, 1, -1, 1, 0};
using Graph=vector<vector<int>>;
ll op(ll a,ll b){return min(a,b);}
ll e(){return 2e9;}
int main(){
	int N;
	cin>>N;
	vector<ll>dp(100);
	dp[0]=1;
	for(int i=1;i<=N;i++){
		if(i>1)dp[i]+=dp[i-2];
		dp[i]+=dp[i-1];
	}
	cout<<dp[N]<<endl;
}