package main

import . "fmt"

func main() {
	var n,c int
	Scan(&n)
	x:=make([]int,n)
	for i:=range x {
		Scan(&x[i])
		if i>1&&isKadomatsu(x[i-2:]) {
			c++
		}
	}
	Println(c)
}

func isKadomatsu(x []int)bool {
	if len(x)<3 {
		return false
	}
	return x[0]!=x[2]&&
	((x[1]>x[0]&&x[1]>x[2])||
	(x[1]<x[0]&&x[1]<x[2]))
}