#include<iostream>

using namespace std;

int n;
int ans;

void f(int k)
{
    if(k==n) ans++;
    else if(k<n)
    {
        f(k+1);
        f(k+2);
    }
}
int main()
{
    cin>>n;
    f(0);  //这里用f(0)
    cout<<ans<<endl;

    return 0;
}