class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next


class Solution:
    def addTwoNumbers(self, l1: ListNode | None, l2: ListNode | None) -> ListNode | None:
        dummy = ListNode()
        curr = dummy
        carry = 0
        while l1 or l2 or carry:
            v1 = l1.val if l1 else 0
            v2 = l2.val if l2 else 0
            digit = (v1 + v2 + carry) % 10
            carry = (v1 + v2 + carry) // 10
            curr.next = ListNode(digit)
            curr = curr.next
            l1 = l1.next if l1 else None
            l2 = l2.next if l2 else None
        return dummy.next