#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <map>
#include <iomanip>
#include <math.h> 
#include <stack>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <tuple>
#include <cctype>
#include <ctype.h>
#include <set>
#include <sstream>

using namespace std;


int main() {
	int i, j, k;
	int n;
	vector<int>a;

	cin >> n;

	for (i = 0; i < n; i++) {
		int num;
		cin >> num;
		a.push_back(num);
	}

	int cnt = 0;

	for (i = 0; i < n - 2; i++) {
		bool flag = false;
		if (a[i] == a[i + 1] || a[i] == a[i + 2] || a[i + 1] == a[i + 2]) continue;
		int num1, num2, num3;

			num1 = a[i];
			num2 = a[i+1];
			num3 = a[i+2];

			int minn = min({ num1,num2,num3 });
			int maxn = max({ num1,num2,num3 });

		if (num2 == maxn || num2 == minn) {
			//cout << num1 << " " << num2 << " " << num3 << endl;
			cnt++;
			//cout << cnt << endl;
		}

	}

	cout << cnt << endl;



	getchar();
	getchar();
	return 0;
}