Given a binary search tree and a number k, write a program to find the largest number in the binary search tree that is less than or equal to k.

Problem Note

If the largest element exists, return its value, else return -1.

Example 1

          27         
          /  \       
         14   35
        / \
       10   19
      / \
     31  42
For the above given binary tree
Input: k = 30
Output: 27
Explanation: 10, 14, 19, and 27 are less than or equal to 30. The largest amongst these numbers is 27.