#include <bits/stdc++.h>
using namespace std;
struct ListNode
{
	int val;
	ListNode *next;
	ListNode() : val(0), next(nullptr) {}
	ListNode(int x) : val(x), next(nullptr) {}
	ListNode(int x, ListNode *next) : val(x), next(next) {}
};
class Solution
{
public:
	ListNode *deleteDuplicates(ListNode *head)
	{
		if (head == nullptr)
		{
			return nullptr;
		}
		ListNode *prev = head;
		ListNode *p = prev->next;
		while (p != nullptr)
		{
			if (p->val != prev->val)
			{
				prev->next = p;
				prev = p;
			}
			p = p->next;
		}
		prev->next = p;
		return head;
	}
};