human
Solve the following python programming problem given the following code:
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def convertBST(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        self.sum = 0
        self.dfs(root)
        return root
        
    def dfs(self, root):
        if root is None:
            return 
        if root.right:
            self.dfs(root.right)
        self.sum += root.val
        root.val = self.sum
        if root.left:
            self.dfs(root.left)
Given the above code, generate some markdown instructions for it.
assistant
#Here is the Python program you requested.

Lecture 4: Basic Algorithms & Data Structure II
Binary Search
Convert BST to Greater Tree
https://leetcode.com/problems/convert-bst-to-greater-tree/description/