Given this binary tree:

Given this binary tree:

    5
   / \
  3   8
 / \
1   4

and the following recursive function to check balance:

def check(node):
    if not node:
        return 0
    left = check(node.left)
    if left == -1:
        return -1
    right = check(node.right)
    if right == -1:
        return -1
    if abs(left - right) > 1:
        return -1
    return max(left, right) + 1

What does check(root) return for this tree?