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

int tab[50005];
int tab2[50005];

int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int n;
	cin >> n;
	for(int i = 0; i < n; i++){
		cin >> tab[i];
		tab2[i] = tab[i];
	}
	int l = 0, w = 1e9;
	for(int i = 0; i < n-1; i++){
		//cout<<tab[i]<<" "<<tab[i+1]<<'\n';
		if(i%2 == 0){
			if(tab[i] >= tab[i+1]){
				//cout<<'a'<<i<<'\n';
				l++;
				tab[i+1] = 1e9;
			}
		}
		else{
			if(tab[i] <= tab[i+1]){
				//cout<<'b'<<i<<'\n';
				l++;
				tab[i+1] = -1e9;
			}
		}
	}
	w = min(w,l);
	l = 0;
	for(int i = 0; i < n-1; i++){
		//cout<<tab2[i]<<" "<<tab2[i+1]<<'\n';
		if(i%2 == 1){
			if(tab2[i] >= tab2[i+1]){
				//cout<<'c'<<i<<'\n';
				l++;
				tab2[i+1] = 1e9;
			}
		}
		else{
			if(tab2[i] <= tab2[i+1]){
				//cout<<'d'<<i<<'\n';
				l++;
				tab2[i+1] = -1e9;
			}
		}
	}
	w = min(w,l);
	cout<<w;
	return 0;
}