class Node():
    def __init__(self, val, next = None):
        self.val = val
        self.next = next


n1 = Node(1, Node(2, Node(3)))
n2 = Node(4, Node(5, Node(9)))


def sum_chain(n1, n2)

    def helper(n1, n2)
        if n1.next and n2.next:
            rest_sum, carry = helper(n1.next, n2.next)

        res_val = n1.val + n2.val + carry

        new_carry = res_val // 10
        res_val = res_val % 10

        return Node(res_val, next=rest_sum), carry

    res, carry = helper(n1, n2)

    if carry == 0:
        return res
    else:
        Node(carry, next=res)