#include <iostream>

using namespace std;
int count;
int n;
int jump(int a){
                            //a 是当前楼层
    if(a == n)  count++;
    else if(a < n) {
        jump(a+1);
        jump(a+2);
    }
    return count; 
}


int main(){


    cin >> n;
    cout << jump(0) << endl;    // 表示从0开始
    return 0;
}