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// Autor: Adam Szymaszkiewicz
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;

LL maxi = 10000000;

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

	int n;
	cin >> n;
	vector<LL> v1(n);
	vector<LL> v2(n);
	for (int i = 0; i < n; i++)
	{
		cin >> v1[i];
		v2[i] = v1[i];
	}

	// 1, -1, 1, -1
	int wyn1 = 0;
	for (int i = 1; i < n; i++)
	{
		if (i%2 == 0)
		{
			if (v1[i-1] >= v1[i])
			{
				v1[i] = maxi;
				wyn1++;
			}
		}
		if (i%2 == 1)
		{
			if (v1[i-1] <= v1[i])
			{
				v1[i] = -maxi;
				wyn1++;
			}
		}
	}

	// -1, 1, -1, 1
	int wyn2 = 0;
	for (int i = 1; i < n; i++)
	{
		if (i%2 == 0)
		{
			if (v2[i-1] <= v2[i])
			{
				v2[i] = -maxi;
				wyn2++;
			}
		}
		if (i%2 == 1)
		{
			if (v2[i-1] >= v2[i])
			{
				v2[i] = maxi;
				wyn2++;
			}
		}
	}

	cout << min(wyn1, wyn2) << "\n";
}