Given a root of a binary tree, find the kth smallest element in the tree.

Input:

$3$

$11$

$14$

$2$

$k=1$

Output: $1$

Explanation: The smallest element in the binary tree is $1.$

Input:

$5$

$11$

$36$

$11$

$24$

$k=3$

Output: $4$

Explanation: The third smallest element in the binary tree is $4.$

$k=5$

Output:$6$

Explanation: There are only $5$ elements in the binary tree. Since $k$ is equal to the

total number of elements, the kth smallest element becomes the largest element,

which is $6$

PLEASE DON'T USE INBUILT FUNCTION,LIBRARY.

DON'T USE VECTOR.

DON'T USE STL