Given a binary tree in which each node element contains a number. Find the maximum possible sum from one leaf node to another.

Example 1:

Input :      
           3                               
         /    \                          
       4       5                     
      /  \      
    -10   4                          

Output: 16

Explanation :
Maximum Sum lies between leaf node 4 and 5.
4 + 4 + 3 + 5 = 16.

Example 2:

Input :    
            -15                               
         /      \                          
        5         6                      
      /  \       / \
    -8    1     3   9
   /  \              \
  2   -3              0
                     / \
                    4  -1
                       /
                     10  

Output :  27

Explanation:
The maximum possible sum from one leaf node 
to another is (3 + 6 + 9 + 0 + -1 + 10 = 27)

Your Task:  
You dont need to read input or print anything. Complete the function maxPathSum() which takes root node as input parameter and returns the maximum sum between 2 leaf nodes.

Expected Time Complexity: O(N)
Expected Auxiliary Space: O(Height of Tree)

Constraints:
1 ≤ N ≤ 10^4