import java.util.*;

class Tut06 {  
    static class Tut06Stack {

        ArrayList<String> list;

        Tut06Stack() {
            list = new ArrayList<>();
        }

        public String toString() {
            return "TODO: Implement toString()";
        }


        int size() {
            return list.size();
        }

        void push(String element) {
        }

        String pop() {
            return null;
        }
        
        String peek() {
            return null;
        }

    }

    static class Tut06Queue {

        ArrayList<String> list;

        Tut06Queue() {
            list = new ArrayList<>();
        }

        public String toString() {
            return "TODO: Implement toString()";
        }


        int size() {
            return list.size();
        }

        void add(String element) {
        }

        String remove() {
            return null;
        }
        
        String peek() {
            return null;
        }

    }

    public static void main(String[] arguments) {
        Tut06Stack stack = new Tut06Stack();
        stack.push("Hello");
        stack.push("Cruel");
        stack.push("World");
        System.out.println(stack.peek()); // World
        System.out.println(stack.size()); // 3
        System.out.println(stack); // ???
        System.out.println(stack.pop()); // World
        System.out.println(stack.pop()); // Cruel
        System.out.println(stack.pop()); // Hello

        System.out.println();
        System.out.println();

        Tut06Queue queue = new Tut06Queue();
        queue.add("Hello");
        queue.add("Cruel");
        queue.add("World");
        System.out.println(queue.peek()); // Hello
        System.out.println(queue.size()); // 3
        System.out.println(queue); // ???
        System.out.println(queue.remove()); // Hello
        System.out.println(queue.remove()); // Cruel
        System.out.println(queue.remove()); // World
    }

}