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#include <bits/stdc++.h>
using namespace std;
int n,w,t1[50007],a,w1;
vector<int>t;
int main()
{
	cin>>n;
	for(int i=0; i<n; i++)
	{
		cin>>a;
		t.push_back(a);
	}
	t1[0]=t[0];
	for(int i=1; i<n; i++)
	{
		t1[i]=t[i];
		if(i%2==1)
		{
			if(t1[i]<=t1[i-1])
			{
				t1[i]=1000007;
				w++;
			}
		}
		else
		{
			if(t1[i]>=t1[i-1])
			{
				t1[i]=-1000007;
				w++;
			}
		}
	}
	t1[0]=t[0];
	w1=w;
	w=0;
	for(int i=1; i<n; i++)
	{
		t1[i]=t[i];
		if(i%2==1)
		{
			if(t1[i]>=t1[i-1])
			{
				t1[i]=-1000007;
				w++;
			}
		}
		else
		{
			if(t1[i]<=t1[i-1])
			{
				t1[i]=1000007;
				w++;
			}
		}
	}
	cout<<min(w,w1)<<"\n";
}