/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode n = null;
        ListNode N = null;
        if (l1 == null){
          return l2;
        }
        else if (l2 == null){
            return l1;
        }
        if (l1 != null && l2 != null){
            if (l1.val < l2.val){
                n = l1;
                l1 = l1.next;
                N = n;
            }
            else if (l1.val > l2.val){
                n = l2;
                l2 = l2.next;
                N = n;
            }
            else if (l1.val == l2.val){
                n = l1;
                l1 = l1.next;
                N = n;
                N.next = l2;
                N = l2;
                l2 = l2.next;
            }
        }
        while (l1 != null && l2 != null){
            if (l1.val < l2.val){
                N.next = l1;
                N = l1;
                l1 = l1.next;
            }
            else if (l1.val > l2.val){
                N.next = l2;
                N = l2;
                l2 = l2.next;
            }
            else if (l1.val == l2.val){
                N.next = l1;
                N = l1;
                l1 = l1.next;
                N.next = l2;
                N = l2;
                l2 = l2.next;
            }
        }
        while (l1 != null){
            N.next = l1;
            N = l1;
            l1 = l1.next;
        }
        while (l2 != null){
            N.next = l2;
            N = l2;
            l2 = l2.next;
        }
        return n;
    }
}