/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;
/**
 * Created by green on 19.12.15.
 */
class steck {
    private int size;
    private Object[] date;
    private int capacity;
    public steck(){
        date = new Object[2];
        capacity = 2;
    }
    public steck(int x){
        date = new Object[x];;
        capacity = x;
    }

    public boolean isEmpty(){
        return size == 0;
    }

    private void resize(int x){
        Object[] newDate = new Object[x];
        System.arraycopy(date, 0, newDate, 0, size);
        date = null;
        date = newDate;
    }

    public void push(Object x){
        if(size == capacity){
            resize(2*capacity);
        }
        date[size++] = x;
    }

    public Object pop(){
        if(isEmpty()){
            return null;
        }
        if(size < capacity/2){
            resize(capacity/2);
        }
        Object temp = date[size -1];
        size = size -1;
        return temp;
    }

    public Object peek(){
        if(isEmpty()) return null;
        return date[size-1];
    }

    public void clear(){
        size = 0;
    }

    public int size(){
        return size;
    }
    public int getCapacity(){
        return size;
    }
}

class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		steck test = new steck(4);
        System.out.println(test.isEmpty());
        test.push(12);
        System.out.println(test.isEmpty());
        System.out.println(test.peek());
        test.push(13);
        test.push(14);
        test.push(15);
        test.push(16);
        test.push(17);
        test.push('(');
        System.out.println(test.size());
        System.out.println(test.peek().equals('('));
        test.pop();
        System.out.println(test.peek());
        test.pop();
        System.out.println(test.peek());
        test.pop();
        System.out.println(test.peek());
        test.pop();
        System.out.println(test.peek());
        test.pop();
        System.out.println(test.peek());
        System.out.println(test.isEmpty());
        test.pop();
        System.out.println(test.peek());
        test.pop();
        System.out.println(test.isEmpty());
	}
}