#include <iostream>
#include <sstream>
#include <math.h>
#include <stack>
#include <set>
#include <algorithm>
#include <string>
#include <queue>
#include <stack>
#include <map>
#include <cstdio>
#include <vector>
using namespace std;

#define INF (1 << 30)
#define INFLL (1LL << 60)

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