object Main {
	def main(args: Array[String]): Unit = {
		val len = io.StdIn.readInt()
		val numsAsStr = io.StdIn.readLine().split(" ")
		val numsAry = new Array[Int](len)
		
		for (str <- numsAsStr) {
			numsAry(numsAsStr.indexOf(str)) = str.toInt
		}
		
		var count = 0
		
		for (num <- 0 until len - 2) {
			if (returnBoolean(Array(numsAry(num), numsAry(num + 1), numsAry(num + 2)))) count += 1
		}
		
		println(count)
	}
	
	def returnBoolean(array: Array[Int]): Boolean = {
		array(1) == array.sortWith((x: Int, y: Int) => x < y)(1)
	}
}