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#include<bits/stdc++.h>
using namespace std;

int tab[100009], tac[100009];

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int n, a, wyn = 1e9;
	cin>>n;
	for(int i=1; i<=n; i++) cin>>tab[i];
	for(int i=1; i<=n; i++) tac[i] = tab[i];
	a = 0;
	for(int i=2; i<=n; i++)
	{
		if(i % 2 == 0 && tac[i] <= tac[i-1])
		{
			tac[i] = 1e9;
			a++;
		}
		else if(i % 2 == 1 && tac[i] >= tac[i-1])
		{
			tac[i] = -(1e9);
			a++;
		}
	}
	if(wyn > a) wyn = a;
	
	for(int i=1; i<=n; i++) tac[i] = tab[i];
	a = 0;
	for(int i=2; i<=n; i++)
	{
		if(i % 2 == 0 && tac[i] >= tac[i-1])
		{
			tac[i] = -(1e9);
			a++;
		}
		else if(i % 2 == 1 && tac[i] <= tac[i-1])
		{
			tac[i] = 1e9;
			a++;
		}
	}
	if(wyn > a) wyn = a;
	
	cout<<wyn;
	return 0;
}