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#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>

int main() {
	std::ios_base::sync_with_stdio(0); std::cin.tie(0); std::cout.tie(0);
	
	int n;
	std::cin >> n;
	
	std::vector<int> input(n);
	
	for (int i = 0; i < n; ++i) {
		std::cin >> input[i];
	}
	
	int nchanges_high = 0;
	bool prev_changed = false;
	for (int i = 1; i < n; ++i) {
		if (i % 2 == 1) {
			if (prev_changed) {
				prev_changed = false;
			} else if (input[i-1] <= input[i]) {
				++nchanges_high;
				prev_changed = true;
			}
		} else {
			if (prev_changed) {
				prev_changed = false;
			} else if (input[i-1] >= input[i]) {
				++nchanges_high;
				prev_changed = true;
			}
		}
	}
	
	int nchanges_low = 0;
	prev_changed = false;
	for (int i = 1; i < n; ++i) {
		if (i % 2 == 1) {
			if (prev_changed) {
				prev_changed = false;
			} else if (input[i-1] >= input[i]) {
				++nchanges_low;
				prev_changed = true;
			}
		} else {
			if (prev_changed) {
				prev_changed = false;
			} else if (input[i-1] <= input[i]) {
				++nchanges_low;
				prev_changed = true;
			}
		}
	}
	
	int answer = std::min(nchanges_low, nchanges_high);
	
	std::cout << answer << '\n';
	
	return 0;
}