#-*- coding: UTF-8 -*-
# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def deleteDuplicates(self, head):
        if head==None or head.next==None:return head
        pre=head
        cur=head.next
        
        while cur!=None:
            if pre.val!=cur.val:
                pre=cur
                cur=cur.next
                continue
            while cur.next!=None and cur.next.val==pre.val:
                cur=cur.next
            
            pre.next=cur.next
            cur=pre.next
        
        return head