#include <iostream>
using namespace std;

int main() {
	
	int n, a=1, b=1, c, ile=0;
	cin >> n;
	
	if (n==1 || n==2)
		cout << ile << endl;
	else
	{
		for (int i=3; i<=n; i++)
		{
			c=a+b;
			if (c%2==0) ile++;
			a=b;
			b=c;
		}
		cout << ile << endl;
	}
	
	
	
	
	return 0;
}