#include <iostream>
using namespace std;

bool func(int a, int b, int c) {
	bool ok = true;
	if (a == b || b == c || c == a) ok = false;
	int nmax = max(a, max(b, c)),
		nmin = min(a, min(b, c));
	if (b != nmax && b != nmin) ok = false;
	return ok;
}

int main(void) {
	int n, a, b, c, tmp;
	cin >> n >> a >> b >> c;
	int ans = 0;
	if (func(a, b, c)) ++ans;
	for (int i = 3; i < n; ++i) {
		cin >> tmp;
		a = b, b = c, c = tmp;
		if (func(a, b, c)) ++ans;
	}
	cout << ans << endl;
	return 0;
}