#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <map>
#include <list>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <iomanip>
#define INF 1050000000
#define SIZE 300
#define MOD 1000000007

using namespace std;


int main()
{
	int n;
	int a[100];
	int cnt = 0;

	cin >> n;

	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}

	for (int i = 0; i < n - 2; i++) {
		if(a[i] < a[i + 1] && a[i + 1] > a[i + 2] && a[i] != a[i + 2]) cnt++;
		if(a[i] > a[i + 1] && a[i + 1] < a[i + 2] && a[i] != a[i + 2]) cnt++;
	}

	cout << cnt << endl;

	return (0);
}