package main

import (
	"fmt"
)

func main() {
	var a [110]int
	var n int
	fmt.Scan(&n)
	for i := 0; i < n; i++ {
		fmt.Scan(&a[i])
	}
	z := 0
	for i := 0; i < n-2; i++ {
		p, q, r := a[i], a[i+1], a[i+2]
		if p == q || q == r || r == p || p < q && q < r || p > q && q > r {
			continue
		}
		z++
	}
	fmt.Println(z)
}