#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <cctype>
using namespace std;
typedef long long ll;

int main()
{
	int n, t[105] = {}, sum = 0;
	set<int>s;
	cin >> n;
	for (int i = 0; i < n; i++)cin >> t[i];
	for (int i = 1; i < n - 1; i++)
	{
		for (int j = i - 1; j <= i + 1; j++)s.insert(t[j]);
		if (static_cast<int>(s.size()) == 3)
		{
			if (t[i]>t[i - 1] && t[i] > t[i + 1])sum++;
			else if (t[i] < t[i - 1] && t[i] < t[i + 1])sum++;
		}
		s.clear();
	}
	cout << sum << endl;
	return 0;
}