Given a binary tree,where each node has value given x, (x>=0).

you need to find maximum sum of nodes's x value ,but you can not select two nodes in the answer such that one node is parent (only immediate),and other is child.

like if 1 is root , and its left child is 2 and right child is 3 ,then you can not include 1 and 2, or 1 and 3 in the answer,but you can include 2-3.

find maximum possible sum...