using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        //Console.WriteLine(evalRPN(new List<string>{"2", "1", "+", "3", "*"}));

        Console.WriteLine(evalRPN(new List<string>{"4", "13", "5", "/", "+"}));

    }

    public static int evalRPN(List<string> tokens){

     if(tokens.Count == 0) return 0;

     var myStack = new Stack<int>();        

        foreach (var i in tokens){

            switch (i){

                case "+":

                     var op1 = myStack.Pop();

                     var op2 = myStack.Pop();

                     var result1 = op1 + op2;

                     myStack.Push(result1);

                     break;

                case "-":

                     var op11 = myStack.Pop();

                     var op22 = myStack.Pop();

                     var result2 = op22 - op11;

                     myStack.Push(result2);

                     break;

                case "*":

                     var op13 = myStack.Pop();

                     var op23 = myStack.Pop();

                     var result3 = op13 * op23;

                     myStack.Push(result3);

                     break;     

                case "/":

                     var op14 = myStack.Pop();

                     var op24 = myStack.Pop();

                     var result4 = op24 / op14;

                     myStack.Push(result4);

                     break;

                default:

                    myStack.Push(int.Parse(i));

                    break;          

            }

        }   

      return myStack.Pop();

​

    }

}