#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int n;
int ans = 0;
void f(int k){
if(k == n){
ans++;
}else if(k < n){
f(k + 1);
f(k + 2);
}
}
int main(){
cin >> n;
f(0);
cout << ans << endl;
return 0;
}