# Merge Two Sorted Lists


# Definition for singly-linked list
class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next


class Solution:
    def mergeTwoLists(self, list1: ListNode, list2: ListNode):
        prehead = ListNode(-1)
        prev = prehead

        while list1 and list2:
            if list1.val <= list2.val:
                prev.next = list1
                list1 = list1.next
            else:
                prev.next = list2
                list2 = list2.next
            prev = prev.next

        return prehead.next