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#include <iostream>
#include <vector>


int main() {
	long count{};
	std::vector<long> numbers;
	std::cin >> count;
	for (long i = 0; i < count; i++) {
		long tmp{};
		std::cin >> tmp;
		numbers.push_back(tmp);
	}
	long countVersion1{};
	long countVersion2{};
	std::vector<bool> version1Changes(numbers.size(), false);
	std::vector<bool> version2Changes(numbers.size(), false);
	for (long i = 1; i < numbers.size(); i++) {
		if (i % 2 == 0) {
			if (numbers[i] > numbers[i - 1]) {
				countVersion1++; // for debugging
			} else if (!version1Changes[i - 1]) {
				version1Changes[i] = true;
			}
			if (numbers[i] < numbers[i - 1]) {
				countVersion2++; // for debugging
			} else if (!version2Changes[i - 1]) {
				version2Changes[i] = true;
			}
		} else {
			if (numbers[i] < numbers[i - 1]) {
				countVersion1++; // for debugging
			} else if (!version1Changes[i - 1]) {
				version1Changes[i] = true;
			}
			if (numbers[i] > numbers[i - 1]) {
				countVersion2++; // for debugging
			} else if (!version2Changes[i - 1]) {
				version2Changes[i] = true;
			}
		}

	}
	long countChanges1{};
	long countChanges2{};
	for (auto c : version1Changes) {
		if (c) {
			countChanges1++;
		}
	}
	for (auto c : version2Changes) {
		if (c) {
			countChanges2++;
		}
	}
	std::cout << std::min(countChanges1, countChanges2) << std::endl;
	return 0;
}