Given a binary search tree and a number N, find the greatest number in the binary search tree that is less than or equal to N.
Example 1 :
Input : N = 24
Output : 21
Explanation : The greatest element in the tree which
is less than or equal to 24, is 21.
(Searching will be like 5->12->21)

Example 2 :
Input : N = 4
Output : 3
Explanation : The greatest element in the tree which
is less than or equal to 4, is 3.
(Searching will be like 5->2->3)
Your task :
You don't need to read input or print anything. Your task is to complete the function findMaxForN() which takes the root of the BST, and the integer N as input paramters and returns the greatest element less than or equal to N in the given BST.

Expected Time Complexity: O(Height of the BST)
Expected Auxiliary Space: O(Height of the BST).
Constraints:
1<=N<=10^{3}

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