def is_kadomatsu? (a, b, c)
  if a == b || b == c || c == a
    return false
  end
  tmp = [a, b, c]
  return b == tmp.max || b == tmp.min
end
gets
arr = gets.chomp.split.map{|str| str.to_i}
count = 0
2.upto(arr.length - 1) {|idx|
  if is_kadomatsu?(arr[idx - 2], arr[idx - 1], arr[idx])
    count += 1
  end
}
puts count