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#include <iostream>
#include <vector>

using namespace std;

constexpr int RANGE = 1e9;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	int n;
	cin >> n;

	vector<int> V(n);
	for (auto& v : V)
		cin >> v;

	auto fun = [n](vector<int> V, bool isHigher) {
		int res = 0;
		for (int i = 0; i < n - 1; i++) {
			if (isHigher) {
				if (V[i] <= V[i + 1]) {
					V[i + 1] = -RANGE;
					res++;
				}
			}
			else {
				if (V[i] >= V[i + 1]) {
					V[i + 1] = RANGE;
					res++;
				}
			}
			isHigher ^= 1;
		}
		return res;
	};

	cout << min(fun(V, true), fun(V, false));
}