# Sum of Nodes with Even Grandparent Values

Given a binary tree `root`

, return the sum of all node values whose grandparents have an even value.

**Constraints**

`0 ≤ n ≤ 100,000`

where`n`

is the number of nodes in`root`

https://binarysearch.com/problems/Sum-of-Nodes-with-Even-Grandparent-Values

## Examples

### Example 1

**Input**

- root =

**Output**

- answer =
`15`

**Explanation**

Nodes `6`

, `7`

, and `2`

have an even value grandparent.

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