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

int main() 
{
	ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    int n,w,mini;
    int *t;
    int *k;
    cin>>n;
    t=new int[n];
    k=new int[n];
    for(int i=0;i<n;++i)
    {
		cin>>t[i];
		k[i]=t[i];
	}
	w=0;
	for(int i=1;i<n;++i)
	{
		if(i%2)
		{
			if(t[i]<=t[i-1])
			{
				++w;
				t[i]=1000000000;
			}
		}
		else
		{
			if(t[i]>=t[i-1])
			{
				++w;
				t[i]=-1000000000;
			}
		}
	}
	mini=w;
	w=0;
	for(int i=1;i<n;++i)
	{
		if(i%2)
		{
			if(k[i]>=k[i-1])
			{
				++w;
				k[i]=-1000000000;
			}
		}
		else
		{
			if(k[i]<=k[i-1])
			{
				++w;
				k[i]=1000000000;
			}
		}
	}
	w=min(mini,w);
	cout<<w<<'\n';
	delete [] t;
	delete [] k;
	return 0;
}