# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def kthSmallest(self, root: Optional[TreeNode], k: int) -> int:
cnt =0
s =[]
cur =root
while cur or s is not None:
while cur :
s.append(cur)
cur =cur.left
cur =s.pop() #1.left
cnt +=1
if(cnt ==k):
return cur.val
cur =cur.right
return -1