#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<ctime>
#include<cctype>
#include<climits>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<memory>
#include<functional>
#include<set>
 
using namespace std;
 
#define ALL(g) (g).begin(),(g).end()
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
#define PP(p) cout<<(p)<<" ";
#define pb push_back
#define mp make_pair
#define INF 1e18

typedef long long ll;
#define int ll
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef vector<char> vc;
typedef pair<int, int> pi;
//int dy[8]={1,1,1,0,-1,-1,-1,0};
//int dx[8]={-1,0,1,1,1,0,-1,-1};
int dx[4]={0,1,0,-1};
int dy[4]={1,0,-1,0};
int mod=1e9+7;

int N,M;
vi a,b;
vi dp;
void input(){
	cin>>N;
	dp.resize(N+1,-1);
}
int dfs(int now){
	if(now==N)return 1;
	if(now>N)return 0;
	if(dp[now]!=-1)return dp[now];
	int ret=0;
	ret+=dfs(now+1);
	ret+=dfs(now+2);
	return dp[now]=ret;
}
signed main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	input();
	P(dfs(0))
	return 0;
}