class Solution {
    int sum=0;
    public int sumEvenGrandparent(TreeNode root) {
        if(root==null) return 0;
        helper(root, null, null);
        return sum;
    }
    
    public void helper(TreeNode node, TreeNode p, TreeNode gp){
        if(node == null) return;
        
        if(gp!=null && gp.val%2==0){
            sum+=node.val;
        }
        
        helper(node.left, node, p);
        helper(node.right, node, p);
    }
}