#include <vector>

#include <iostream>

#include <algorithm>

using namespace std;

#define REP(i,n) for(int i=0;i<(n);++i)

#define FOR(i,a,b) for(int i=(a);i<=(b);++i)

#define RFOR(i,a,b) for(int i=(a);i>=(b);--i)

typedef long long LL;

struct ListNode {

int val;

ListNode *next;

ListNode() : val(0), next(NULL) {}

ListNode(int x) : val(x), next(NULL) {}

};

class Solution {

ListNode *deleteDuplicates(ListNode *head) {

ListNode *ret = NULL, *prev = NULL;

if (head == NULL) return ret;

while (head != NULL) {

int now = head->val;

if (head->next != NULL && head->next->val == now) {

while (head != NULL && head->val == now) head = head->next;

} else {

if (ret == NULL) {

ret = head;

prev = head;

} else {

prev->next = head;

prev = head;

}

head = head->next;

}

}

if (prev != NULL) prev->next = NULL;

return ret;

}

};

int main() {

ListNode mm[7];

mm[0] = ListNode(1);

mm[1] = ListNode(1);

mm[2] = ListNode(1);

mm[3] = ListNode(2);

mm[4] = ListNode(3);

mm[5] = ListNode(4);

mm[6] = ListNode(5);

REP(i,4) mm[i].next = &mm[i + 1];

Solution s;

ListNode *ret = s.deleteDuplicates(&mm[0]);

while (ret != NULL) {

cout << ret->val << endl;

ret = ret->next;

}

return 0;

}