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

int main() {
	int N;
	cin >> N;

	vector<int> v(N);
	for (int i = 0; i < N; i++) {
		cin >> v.at(i);
	}

	int cnt = 0;
	for (int i = 1; i < N - 1; i++) {
		int a = v.at(i - 1),
			b = v.at(i),
			c = v.at(i + 1);
		int MIN = min(a, min(b, c)),
			MAX = max(a, max(b, c));
		//cout << a << ' ' << b << ' ' << c << endl;
		//cout << MIN << ' ' << MAX << endl;

		if ((a != b) && (a != c) && (b != c)) {
			if ((b == MIN) || (b == MAX)) {
				cnt++;
			}
		}
	}

	cout << cnt << endl;
}