// used to gain access to System.out
import java.io.*;

public class Stack {
  // place to store data (an example of a one line comment)
  private int [] data;

  /* how many things are currently in the stack.
     (example of multi line comment)
  */
  private int stack_size = 0;
  
  // constructor
  public Stack(int size) {
    // this is where you actually create the array.
    // it does not exist before here.
    data = new int[size];
  }

  // maybe should return a boolean to indicate success
  public void push(int new_top) {
    // insert the data into the array
    data[stack_size] = new_top;
    // increment the current count
    stack_size++;
  }

  public int pop() {
    // decrease the current count.
    // you could also do this later but it makes it a bit more compact
    // if you do it here.
    stack_size--;
    // return the value to the user
    return data[stack_size];
  }

  // the program that actually runs the program
  public static void main(String[ ] args) {
    // create the Stack
    Stack s = new Stack(3);
    // add some data
    s.push(1);
    s.push(2);
    s.push(3);
    // print out some data
    System.out.println(s.pop());
    System.out.println(s.pop());
  }
}