#include<iostream>
#include<string>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<cmath>
#include<vector>
#include<utility>
#define FOR(i, a, b) for(int i=(a);i<=(b);i++)
#define RFOR(i, a, b) for(int i=(a);i>=(b);i--)
#define MOD 1000000007

using namespace std;


int main(void) {
	int n;
	int a[101];
	int count = 0;
	cin >> n;
	FOR(i, 1, n) {
		cin >> a[i];
	}
	FOR(i, 1, n - 2) {
		if (!((a[i] < a[i + 1]) && (a[i + 1] < a[i + 2]))) {
			if ((a[i + 2] - a[i + 1] != 0) && (a[i + 1] - a[i] != 0) && (a[i + 2] - a[i] != 0)) {
				count++;
			}
			
		}
	}
	cout << count << endl;
	return 0;
}