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// 2022-1-orn-ornitolog-2.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>

constexpr int BIG = 1e7;
constexpr int SMALL = -1e7;

int main()
{
	std::ios_base::sync_with_stdio(0);
	std::cin.tie(0);
	std::cout.tie(0);

	int n, prev, l, a = 0, b = 0, aprev, bprev, al, bl;
	std::cin >> n >> prev;
	aprev = prev;
	bprev = prev;
	for (int i = 1; i < n; i++) {
		std::cin >> l;
		al = l;
		if (i % 2) { // gora
			if (al <= aprev) {
				al = BIG;
				a++;
			}
		}
		else { // dol
			if (al >= aprev) {
				al = SMALL;
				a++;
			}
		}
		aprev = al;

		bl = l;
		if (i % 2 == 0) { // gora
			if (bl <= bprev) {
				bl = BIG;
				b++;
			}
		}
		else
		{
			if (bl >= bprev) {
				bl = SMALL;
				b++;
			}
		}
		bprev = bl;
	}
	std::cout << std::min(a, b) << '\n';
}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

// Tips for Getting Started: 
//   1. Use the Solution Explorer window to add/manage files
//   2. Use the Team Explorer window to connect to source control
//   3. Use the Output window to see build output and other messages
//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file