#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;

int main(){
	int n;
	int cnt=0;
	cin >> n;
	int a[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]){
			if((a[i]<a[i+1]&&a[i+1]>a[i+2])||(a[i]>a[i+1]&&a[i+1]<a[i+2]))cnt++;
		}
	}
	cout << cnt << endl;
}