using System;
using System.Collections.Generic;

namespace calculator
{
  class Program
  {
    static void Main(string[] args)
    {
      if (args.Length == 0)
        Console.WriteLine("REPL is not ready yet. Please, provide mathematic expression as an argument");
      else
        try
        {
          string[] expr = args[0].Split();
          Stack<double> st = new Stack<double>();

          for (int i = 0; i < expr.Length; i++)
          {
            object val = convertOne(expr[i]);

            if (val is double number)
              st.Push(number);
            else if (val is char oper)
            {
              try
              {
                double b = st.Pop();
                double a = st.Pop();
                switch (oper)
                {
                  case '+':
                    st.Push(a + b);
                    break;
                  case '-':
                    st.Push(a - b);
                    break;
                  case '*':
                    st.Push(a * b);
                    break;
                  case '/':
                    st.Push(a / b);
                    break;
                  case '^':
                    st.Push(Math.Pow(a, b));
                    break;
                  default:
                    throw new Exception("Got unknown operator");
                }
              }
              catch (InvalidOperationException)
              {
                throw new Exception(oper + " operation requires two operands");
              }
            }
            else throw new Exception("Stack corrupted");
          }

          Console.WriteLine(st.Pop());
        }
        catch (Exception e)
        {
          Console.WriteLine(e.Message);
        }
    }

    static private object convertOne(string s)
    {
      double res;
      if (Double.TryParse(s, out res)) return res;
      else if (s.Length == 1) return s[0];
      else throw new Exception("Got multiple characters operator");
    }
  }
}