/**
 * 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 dhead = new ListNode(-1);
        ListNode r = dhead;
        while(l1!=null&&l2!=null){
            if(l1.val<=l2.val){
                r.next = l1;
                r = l1;
                l1 = l1.next;
            }else{
                r.next = l2;
                r = l2;
                l2 = l2.next;
            }
        }
        if(l1!=null)
            r.next = l1;
        if(l2!=null)
            r.next = l2;

        return dhead.next;
    }
}