using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Tutorials
{
    class Program
    {
        static void Main(string[] args)
        {
            int numAmount = 0;
            int numCount = 0;
            int equationCount = 0;
            double firstValue = 0.0;
            double nextValue = 0.0;
            string equationMark;

        Start:
            numAmount = 0;
            numCount = 0;
            equationCount = 0;
            Console.Write("Write the amount of numbers: ");

            try
            {
                numAmount = Convert.ToInt32(Console.ReadLine());
            }

            catch (FormatException)
            {
                Console.WriteLine("ERROR: Number required");
                Console.WriteLine();
                goto Start;
            }
            Console.WriteLine();

            List < double > numStore = new List<double>();

            for (int i = 0; i < numAmount; i++)
            {
                numCount++;
                Console.Write("Number " + numCount + ": ");

                if(i%2 == 0)
                {
                    try
                    {
                        nextValue = Convert.ToDouble(Console.ReadLine());
                    }

                    catch (FormatException)
                    {
                        Console.WriteLine("ERROR: Number required");
                        Console.WriteLine();
                        goto Start;
                    }
                    numStore.Add(nextValue);
                } else
                {
                    try
                    {
                        firstValue = Convert.ToDouble(Console.ReadLine());
                    }

                    catch (FormatException)
                    {
                        Console.WriteLine("ERROR: Number required");
                        Console.WriteLine();
                        goto Start;
                    }
                    numStore.Add(firstValue);
                }

                if(i != numAmount)
                {
                    Console.Write("Equation mark(+,-,*,/): ");
                    equationMark = Convert.ToString(Console.ReadLine());
                }

                if (equationMark == "+" || (equationMark == "-" || (equationMark == "*" || (equationMark == "/"))))
                {
                    if (equationMark == "+")
                    {
                        firstValue = firstValue + nextValue;
                    }

                    if (equationMark == "-")
                    {
                        equationCount = 2;
                    }

                    if (equationMark == "*")
                    {
                        equationCount = 3;
                    }

                    if (equationMark == "/")
                    {
                        equationCount = 4;
                    }
                } else
                {
                    Console.WriteLine("ERROR: Invalid equation mark.");
                    Console.WriteLine();
                    goto Start;
                }
                Console.WriteLine();
            }
            Console.WriteLine("Result: " + firstValue);
            Console.ReadKey();
        }
    }
}