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//Solution by Mikołaj Kołek

#include "bits/stdc++.h"
#define intin *istream_iterator<int>(cin)

using namespace std;

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	
	int n = intin;
	vector<int> a(n);
	copy_n(istream_iterator<int>(cin), n, a.begin());
	
	int bestRes = INT_MAX, res = 0;
	
	int lastChar = a[0], streak = 0;
	for(int i = 1; i < n; i++) {
		if(((i % 2 == 0) and a[i] <= lastChar) or ((i % 2 == 1) and a[i] >= lastChar)) {
			streak++;
		}
		else { 
			res += (streak + 1) / 2;
			streak = 0;
		}
		
		lastChar = a[i];
	}
	bestRes = min(res + ((streak + 1) / 2), bestRes);
	
	lastChar = a[0], streak = 0, res = 0;
	for(int i = 1; i < n; i++) {
		if(((i % 2 == 1) and a[i] <= lastChar) or ((i % 2 == 0) and a[i] >= lastChar)) {
			streak++;
		}
		else {	
			res += (streak + 1) / 2;
			streak = 0;
		}
		
		lastChar = a[i];
	}
	bestRes = min(res + ((streak + 1) / 2), bestRes);
	
	cout << bestRes;
	
	return 0;
}