Copied the code given to the workspace and received a FormatException error.

using System;

namespace Treehouse.FitnessFrog
{
    class Program
    {
        static void Main()
        {
            int runningTotal = 0;

            bool keepGoing = true;
            while(keepGoing)
            {
                // Prompt user for minutes exercised 
                Console.Write("Enter how many minutes you exercised or type \"quit\" to exit: ");
                string entry = Console.ReadLine();        

                if(entry == "quit")
                {
                    keepGoing = false;
                }
                else
                {
                    // Add minutes exercised to total 
                    int minutes = int.Parse(entry);

                    if (minutes <= 0)
                    {
                      Console.WriteLine(minutes + " is not an acceptable value.");
                      continue;
                    }

                    else if(minutes <= 10)
                    {
                        Console.WriteLine("Better than nothing, am I right?");
                    }
                    else if(minutes <= 30)
                    {
                        Console.WriteLine("Way to go hot stuff!");
                    }
                    else if(minutes <= 60)
                    {
                        Console.WriteLine("You must be a ninja warrior in training!");
                    }
                    else
                    {        
                        Console.WriteLine("Okay, now you're just showing off!");
                    }

                    runningTotal = runningTotal + minutes;

                    // Display total minutes exercised to the screen 
                    Console.WriteLine("You've entered " + runningTotal + " minutes.");
                }
                // Repeat until user quits
            }

            Console.WriteLine("Goodbye");
        }
    }
}