using System;

using System.Collections;   

using System.Linq;

​

public class OperationInvalidException: Exception

{

}

​

public class WordMachine 

{

​

    protected Stack stack = new Stack();

​

    protected String[] allowedOperations = { "dup", "pop", "+", "-" };

​

    protected String commandLine = "";

    public WordMachine(String commandLine)

    {

        this.commandLine = commandLine;

    }

    public bool IsOperationAllowed(String operation)

    {

        String normalizedOperation = operation.ToLower();

​

        int n = 0;

        bool isNumeric = int.TryParse(normalizedOperation, out n);

        if(isNumeric) return true;

        else if(allowedOperations.Contains(normalizedOperation)) return true;

        else return false;

    }

​

    protected void ProcessOperation(String operation)

    {

​

        String normalizedOperation = operation.ToLower();

        if(!IsOperationAllowed(normalizedOperation)) throw new OperationInvalidException();

​

        int n = 0;

        bool isNumeric = int.TryParse(normalizedOperation, out n);

​

        if(isNumeric) 

        {

            stack.Push(normalizedOperation);

            Console.WriteLine("push  " + normalizedOperation);

        }

        else

        {

            String peek = "";

            switch (normalizedOperation) { 

                case "dup": 

                    if(stack.Count == 0) throw new OperationInvalidException();

                    peek = (String)stack.Peek();

                    stack.Push(peek);

                    Console.WriteLine("dup " + peek);

                    break; 

​

                case "pop": 

                    //Console.WriteLine("POP: stack.Count = " + stack.Count);

                    if(stack.Count == 0) throw new OperationInvalidException();

​

                    peek = (String)stack.Peek();

                    stack.Pop();

​

                    Console.WriteLine("pop " + peek);

                    break; 

​

                case "+": 

                    //Console.WriteLine("+: stack.Count = " + stack.Count);

                    if(stack.Count < 2) throw new OperationInvalidException();

                    int sum = Int32.Parse((String)stack.Pop()) + Int32.Parse((String)stack.Pop());

                    stack.Push(sum.ToString());

                    break; 

                case "-": 

                    //Console.WriteLine("-: stack.Count = " + stack.Count);

                    if(stack.Count < 2) throw new OperationInvalidException();

                    int difference = Int32.Parse((String)stack.Pop()) - Int32.Parse((String)stack.Pop());

                    if(difference < 0) throw new OperationInvalidException();

                    else stack.Push(difference.ToString());

                    break; 

​

                default: throw new OperationInvalidException();

            }

        }

        //Console.WriteLine(operation + "- stack.Count = " + stack.Count);

        printStack();

        Console.WriteLine("-----------------------------------------------");

​

    }

    private void printStack()

    {

        foreach(String s in stack)

        {

            Console.WriteLine("Item: " + s);

        }

    }

    public int execute()

    {

        String[] operations = commandLine.Split(' ');  

        foreach(var operation in operations)

        {

            try

            {

                ProcessOperation(operation);

            }

            catch(OperationInvalidException)

            {

                Console.WriteLine("Operation not allowed: " + operation);

                return -1;

            }

        }

​

        if(stack.Count == 0) return -1;

        else return Int32.Parse((String)stack.Peek());

    }

}

​

public class Solution {

    public int solution(String s)

    {

        WordMachine wordMachine = new WordMachine(s);

        return wordMachine.execute();       

    }

}

​

​

public class Program

{

    public static void Main()

    {

        //String instruction = "13 DUP 4 POP 5 DUP + DUP + -";

        //String instruction = "3 DUP 5 - -";

        String instruction = "5 6 + -";

        Solution solution = new Solution();

​

        Console.WriteLine("Solution 1 = " + solution.solution(instruction));

    }

}