func main()
	var N: int :: cui@input().toInt(&)
	var _: [][]char :: cui@input().split(" ")
	var A: []int :: #[N]int
	for i(0, N - 1)
		do A[i] :: _[i].toInt(&)
	end for
	var ans: int
	for i(0, N - 3)
		if(A[i] = A[i + 2])
			skip i
		end if
		if(A[i] < A[i + 1] & A[i + 1] > A[i + 2])
			do ans :+ 1
		elif(A[i] > A[i + 1] & A[i + 1] < A[i + 2])
			do ans :+ 1
		end if
	end for
	do cui@print("\{ans}\n")
end func