Q20

The postorder traversal of a binary tree is $\text{8, 9, 6, 7, 4, 5, 2, 3, 1}$. The inorder traversal of the same tree is ${8, 6, 9, 4, 7, 2, 5, 1, 3}$. The height of a tree is the length of the longest path from the root to any leaf. The height of the binary tree above is _____