Given a Binary Search Tree. Find sum of all elements smaller than and equal to Kth smallest element.
Example 1:
Input:
20
/ \
8 22
/ \
4 12
/ \
10 14 , K=3
Output: 22
Explanation:
Sum of 3 smallest elements are:
4 + 8 + 10 = 22
Example 2:
Input:
10
/ \
5 11
/ \
4 7
\
8 , K=2
Output: 9
Explanation:
The sum of two smallest elements
is 4+5=9.

Your task:
You don't need to read input or print anything. Your task is to complete the function sum() which takes the root node and an integer K as input parameters and returns the sum of all elements smaller than and equal to kth smallest element.

Expected Time Complexity: O(K)
Expected Auxiliary Space: O(1)

Constraints:
1<=Number of nodes in BST<=100
1<=K<=N

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