#include <iostream>
using namespace std;

class Node {
public:
	int data;
	Node *next;
    
	Node(int data){
		this->data = data;
		this->next = NULL;
	}
    
    ~Node() {
		delete next;
	}
};

void deleteAlternateNodes(Node *head) {
    Node *p = head, *q;
    while ((p != NULL) && (p->next != NULL)) {
        q = p->next;
        p->next = q->next;
        q->next = NULL;
        delete q;
        p = p->next;
    }
}

Node* takeinput() {
    int data;
    Node *head = NULL, *tail = NULL;
    while ((cin >> data) && (data != -1)) {
        Node *newNode = new Node(data);
        if (head == NULL) {
            head = newNode;
        }
        else {
            tail->next = newNode;
        }
		tail = newNode;
    }
    return head;
}

void print(Node *head) {
	while (head != NULL) {
		cout << head->data << ' ';
		head = head->next;
	}
	cout << endl;
}

int main() {
    Node *head = takeinput();
    print(head);
    deleteAlternateNodes(head);
    print(head);
    delete head;
    return 0;
}