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//Dawid Lebryk
#include <iostream>

using namespace std;
const int MAXN = 50000, minA = -1e9, maxA = 1e9;

int tab[MAXN + 5];
int tab1[MAXN + 5];
int tab2[MAXN + 5];

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int n;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> tab[i];
	}

	//maleje rosnie
	int w1 = 0;
	tab1[0] = tab[0];
	for (int i = 1; i < n; i++)
	{
		tab1[i] = tab[i];
		if (i % 2 == 0)
		{
			if (tab1[i] <= tab1[i - 1])
			{
				tab1[i] = maxA;
				w1++;
			}
		}
		else
		{
			if (tab1[i] >= tab1[i - 1])
			{
				tab1[i] = minA;
				w1++;
			}
		}
	}

	//rosnie maleje
	int w2 = 0;
	tab2[0] = tab[0];
	for (int i = 1; i < n; i++)
	{
		tab2[i] = tab[i];
		if (i % 2 == 0)
		{
			if (tab2[i] >= tab2[i - 1])
			{
				tab2[i] = minA;
				w2++;
			}
		}
		else
		{
			if (tab2[i] <= tab2[i - 1])
			{
				tab2[i] = maxA;
				w2++;
			}
		}
	}
	cout << min(w1, w2);
}