/**
 * 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 mergeNodes(ListNode head) {
        ListNode tail = head;
        for(ListNode cur = head.next; cur.next != null; cur = cur.next){
            if(cur.val != 0){
                tail.val += cur.val;
            }
            else
            {
                tail = tail.next;
                tail.val = 0;
            }
        }

        tail.next = null;
        return head;
    }
}