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// Grzegorz Ryn
// Jagiellonian University

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define st first
#define nd second
#define all(__VAR) (__VAR).begin(), (__VAR).end()
#define DEBUG(__VAR) cout << #__VAR << ": " << __VAR << endl;

template <typename T, typename U>
ostream & operator<<(ostream &out, const pair<T, U> &var) {
	cout << "{" << var.st << ", " << var.nd << "}";
	return out;
}

template <typename T>
ostream & operator<<(ostream &out, const vector<T> &var) {
	cout << "[";
	for(int i=0; i<(int)var.size()-1; i++) {
		cout << var[i] << ", ";
	}
	if(var.size()>0)
		cout << var.back();
	cout << "]" << endl;
	
	return out;
}

const int inf = 1'000'000'000;

int solve(vector<int> a, bool rise) {
	int N = a.size(), result = 0;

	for(int i=0; i<N-1; i++) {
		if(rise) {
			if(a[i] < a[i+1]) {
				
			}
			else {
				a[i+1] = inf;
				result++;
			}
		}
		else {
			if(a[i] > a[i+1]) {

			}
			else {
				a[i+1] = -inf;
				result++;
			}
		}
		rise ^= 1;
	}



	return result;
}

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	
	int N;
	cin >> N;
	vector<int> a(N);
	for(int i=0; i<N; i++) {
		cin >> a[i];
	}

	cout << min(solve(a, 0), solve(a, 1)) << '\n';

	return 0;
}