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#include <bits/stdc++.h>

using namespace std;

const int MAX = 50007;
int decr[MAX];
int incr[MAX];

int main(void)
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);

	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		int temp;
		cin >> temp;
		decr[i] = temp;
		incr[i] = temp;
	}

	// zalozmy ze pierwszy musi malec
	int count_d = 0;
	for (int i = 1; i < n; i++) {
		if ((i % 2) and decr[i] >= decr[i - 1]) {
			count_d++;
			decr[i] = -INT_MAX;
		}
		else if ((i % 2 == 0) and decr[i] <= decr[i - 1]) {
			count_d++;
			decr[i] = INT_MAX;
		}
	}

	// zalozmy ze pierwszy musi rosnac
	int count_a = 0;
	for (int i = 1; i < n; i++) {
		if ((i % 2) and incr[i] <= incr[i - 1]) {
			count_a++;
			incr[i] = INT_MAX;
		}
		else if ((i % 2 == 0) and incr[i] >= incr[i - 1]) {
			count_a++;
			incr[i] = -INT_MAX;
		}
	}

	cout << min(count_a, count_d) << '\n';

	return 0;
}