#define tracing

using System;
using System.Diagnostics;

class Trace {
  
  [Conditional("tracing")]
  public static void WriteLine(string s) {
    Console.WriteLine(s);
  }
  
  [Conditional("tracing")]
  public static void WriteLine() {
    Console.WriteLine();
  }
  
  [Conditional("tracing")]
  public static void Write(string s) {
    Console.Write(s);
  }
  
}

class Stack {
  int[] data = new int[16];
  int top = 0;
  
  [Conditional("tracing")]
  void Dump() {
    for (int i = 0; i < top; i++)
      Console.Write(data[i] + " ");
    Console.WriteLine();
  }
  
  public void Push(int x) {
    Trace.Write("Push(" + x + "): ");
    if (top < 16) {
      data[top] = x; top++;
    } else throw new OverflowException();
    Dump();
  }
  
  public int Pop() {
    Trace.Write("Pop(): ");
    if (top == 0) throw new UnderflowException();
    top--;
    Dump();
    return data[top];
  }
  
  public int Size {
    get { return top; }
  }
}

class OverflowException: ApplicationException {}
class UnderflowException: ApplicationException {}

public class Test {

  public static void Main() {
    Stack stack = new Stack();
    for (int i = 0; i < 5; i++)
      stack.Push(i);
    while (stack.Size > 1) {
      stack.Push(stack.Pop() + stack.Pop());
    }
    Console.WriteLine("result = " + stack.Pop());
  }
}