#include<bits/stdc++.h>
using namespace std;
long long many = 0;
void fly(long long numb, long long end)
{
	if(numb >= end)
	{
		if(numb == end) many += 1;
	}
	else
	{
		fly(numb + 1, end);
		fly(numb + 2, end);
	}
}
int main()
{
	long long end;
	cin >> end;
	fly(1, end);
	cout << many << endl;
	return 0;
}