Remove duplicate in sorted linked list - not optimized for run time - could not figure out - 2nd practice

EMDUPLNK2.java

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     public int val;
 *     public ListNode next;
 *     ListNode(int x) { val = x; next = null; }
 * }
 */
public class Solution {
	public ListNode deleteDuplicates(ListNode a) {
	    if(a==null)
	        return null; 
	  
	    if(a.next == null)
	        return a;
	    
	    
	    ListNode runner = a; 
	    
	    while(true)
	    {
	        // skip duplicate node, such as 1, 1, 1, 2, skip second 1, third 1
	        ListNode start = runner; 
	        while( start.val == runner.next.val)
	        {
	            runner = runner.next; 
	            if(runner == null)
	            {
	                return a; 
	            }
	        }
	          
	        start.next = runner;  
	        if(runner.next == null)
	            return a; 
	    }
	    
	    return a;  
	}
    
}