#include <bits/stdc++.h>

using namespace std;

int N;
long long dp[50] = {0};

long long rec(int number = 0){
    
    if(number > N) return 0;
    if(number == N) return 1;
    
    long long &res = dp[number];
    if(res != 0) return res;
    
    res += rec(number + 1);
    res += rec(number + 2);
    
    return res;
}

int main(void){
    
    cin >> N;
    
    cout << rec() << endl;
    
    return 0;
}