package main

import "fmt"

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func main() {
	var N int
	fmt.Scan(&N)
	A := make([]int, N)
	for i := range A {
		fmt.Scan(&A[i])
	}
	var ans int
	for i := 0; i+2 < N; i++ {
		maxk := max(A[i], max(A[i+1], A[i+2]))
		mink := min(A[i], min(A[i+1], A[i+2]))
		midk := A[i] + A[i+1] + A[i+2] - (maxk + mink)
		if maxk != mink && mink != midk && midk != maxk &&
			(midk == A[i] || midk == A[i+2]) {
			ans++
		}
	}
	fmt.Println(ans)
}