class Solution {
    int sum=0;
    public int rangeSumBST(TreeNode root, int low, int high) {
        
        if(root == null) {
            return 0;
        }
        if(low<=root.val&&high>=root.val) sum+=root.val;
        
        if(root.val>low){
            rangeSumBST(root.left, low, high);
        }
        if(root.val<=high){
            rangeSumBST(root.right, low, high);
        }
        
        return sum;
    }
}