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#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

/**
	Helpful links
	https://www.geeksforgeeks.org/longest-alternating-subsequence/
	https://leetcode.com/problems/decrease-elements-to-make-array-zigzag/
	https://en.wikipedia.org/wiki/Alternating_permutation
*/

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	int n, count1 = 0, count2 = 0;

	cin >> n;

	vector<int> vect(n);

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

	for (int i = 0; i < n - 1; i++)
	{
		if (i % 2 == 0 && vect[i] <= vect[i + 1]) {
			count1++;
			i++;
			continue;
		}

		if (i % 2 == 1 && vect[i] >= vect[i + 1]) {
			count1++;
			i++;
			continue;
		}
	}

	for (int i = 0; i < n - 1; i++)
	{
		if (i % 2 == 0 && vect[i] >= vect[i + 1]) {
			count2++;
			i++;
			continue;
		}

		if (i % 2 == 1 && vect[i] <= vect[i + 1]) {
			count2++;
			i++;
			continue;
		}
	}

	cout << min(count1, count2);
}