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