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#include <iostream>
#include <vector>

using namespace std;

#define SMALL -1000000000
#define BIG 1000000000

void debug(vector<int> v) {
	for (auto i : v) {
		cout << i << ' ';
	}
	cout << '\n';
}

int main() {
	int n;
	cin >> n;
	vector<int> v1(n), v2(n);
	for (int i = 0; i < n; ++i) {
		int a;
		cin >> a;
		v2[i] = v1[i] = a;
		// cout << v1[n] << ' ';
	}
	// debug(v1);

	int low_high = 0;
	for (int i = 1; i < n; ++i) {
		if ((i % 2 == 0) && (v1[i] >= v1[i - 1])) {
			// cout << "here v1 if " << i << '\n';
			v1[i] = SMALL;
			++low_high;
		} else if ((i % 2 != 0) && (v1[i] <= v1[i - 1])) {
			// cout << "here v1 else " << i << '\n';
			v1[i] = BIG;
			++low_high;
		}
	}
	// debug(v1);

	int high_low = 0;
	for (int i = 1; i < n; ++i) {
		if ((i % 2 == 0) && (v2[i] <= v2[i - 1])) {
			v2[i] = BIG;
			++high_low;
		} else if ((i % 2 != 0) && (v2[i] >= v2[i - 1])) {
			v2[i] = SMALL;
			++high_low;
		}
	}
	// debug(v2);

	cout << min(low_high, high_low) << endl;
	return 0;
}