import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定,请勿修改,直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode deleteDuplicates (ListNode head) {
        // write code here
        if(head==null||head.next==null) return head;
        ListNode p=head;
        ListNode temp=p;
        while(p.next!=null){
            

            p=p.next;
            if(p.val==temp.val) {
                temp.next=p.next;
            }else temp=p;
        }
        return head;
    }
}