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#include <bits/stdc++.h>
using namespace std;

constexpr int INF = 1'000'000'000;

int calc(vector<int> a) {
	int result = 0;
	for (int i = 1; i < (int) a.size(); i++) {
		if (i % 2 == 0) {
			if (!(a[i] > a[i - 1])) {
				a[i] = INF;
				result++;
			}
		}
		else {
			if (!(a[i] < a[i - 1])) {
				a[i] = -INF;
				result++;
			}
		}
	}
	return result;
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int n;
	cin >> n;
	
	vector<int> a(n), a_negative(n);
	for (int i = 0; i < n; i++) {
		cin >> a[i];
		a_negative[i] = -a[i];
	}
	
	cout << min(calc(a), calc(a_negative)) << '\n';
	
	return 0;
}