# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        isaddone = 0
        answer = ListNode(0)
        result = answer
        while True:
            if isaddone == 0:
                numsum = l1.val + l2.val 
            else:
                numsum = l1.val + l2.val + 1
            
            if numsum > 9 and (l1.next != None or l2.next != None):
                answer.val = numsum % 10
                isaddone = 1
            elif numsum > 9 and l1.next == None and l2.next == None:
                answer.val = numsum % 10
                answer.next = ListNode(1)
                break
            elif numsum < 10 and (l1.next != None or l2.next != None):
                answer.val = numsum
                isaddone = 0          
            elif numsum < 10 and l1.next == None and l2.next == None:
                answer.val = numsum
                break

            if l1.next != None:
                l1 = l1.next
            else:
                l1 = ListNode(0)

            if l2.next != None:
                l2 = l2.next
            else:
                l2 = ListNode(0)
            
            answer.next = ListNode(0)
            answer = answer.next
            
        return result