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

int main (){
	
	int n, wyn=0, tab[50010], wyn2=0;
	
	cin>>n;
	
	for (int i=0; i<n; i++) cin>>tab[i];
	
	for (int i=1; i<n; i++){
		if(i%2==0 and tab[i-1]<=tab[i]) wyn++, i++;
		else if(i%2==1 and tab[i-1]>=tab[i]) wyn++, i++; 
	}
	
	for (int i=1; i<n; i++){
		if(i%2==0 and tab[i-1]>=tab[i]) wyn2++, i++; 
		else if(i%2==1 and tab[i-1]<=tab[i]) wyn2++, i++;
		
	}
	cout<<min(wyn, wyn2);
	
	return 0;
}