#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <time.h>
 
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define FFOR(i,a,b) for(int i=(a);i<=(b);i++)
#define REP(i,b) FOR(i,0,b)
#define RREP(i,b) FFOR(i,1,b)
#define PB push_back
#define F first
#define S second
#define BE(c) c.begin(),c.end()
using namespace std;
typedef long long LL;
typedef LL ut;
typedef long double ld;
typedef pair<ut,ut> pr;
typedef vector<pr> Vpr;
typedef vector<ut> VI;
typedef pair<ut,pr> ppr;
typedef priority_queue<pr,Vpr, greater<pr> > PQ;
const int SIZE=1e+5 + 1;
const ut INF=1<<29;

const ld eps=1e-6;
const LL mod=1e+6 + 3;

int N;
LL memo[128];

LL rec(int n){
	if(memo[n] != -1)
		return memo[n];
	
	if(n == N)
		return 1;
	LL res = 0;
	res = rec(n + 1);
	if(n + 2 <= N)
		res += rec(n + 2);
	return memo[n] = res;
}

int main() {
	cin.tie(0);
    ios::sync_with_stdio(false);
    memset(memo, -1, sizeof(memo));
    
    cin >> N;
    cout << rec(0) << endl;
 	return 0;
}