using System;

​

namespace MyProgram

{

    public class Program

    {

        public static void Main() {

           Console.WriteLine(formatDuration(39999999));

           Console.WriteLine(formatDuration(99));

           Console.WriteLine(formatDuration(99999));

        Console.WriteLine(formatDuration(7200));

        Console.WriteLine(formatDuration(3));

        Console.WriteLine(formatDuration(1));

        Console.WriteLine(formatDuration(3600));

        Console.WriteLine(formatDuration(86400));

        Console.WriteLine(formatDuration(31557600));

        }

​

  static string formatDuration (int seconds) {

  var result = "";

  if (seconds >= 31557600){

    var years = seconds / 31557600;

    seconds = seconds - years * 31557600;

    result += years.ToString() + " year";

    result += years > 1 ? "s" : "";

  }

  if (seconds >= 86400){

      if(result.Length > 0)

      {

          result += ", ";

      }

    var days = seconds / 86400;

    seconds = seconds - (days * 86400);

    result += days.ToString() + " day";

    result += days > 1 ? "s" : "";

  }

  if (seconds >= 3600){

      if(result.Length > 0)

      {

          result += ", ";

      }

    var hours = seconds / 3600;

    seconds -= hours * 3600;

    result += hours.ToString() + " hour";

    result += hours > 1 ? "s" : "";

  }

  if (seconds > 60){

      if(result.Length > 0)

      {

          result += ", ";

      }

    var minutes = seconds / 60;

    seconds -= minutes * 60;

    result += minutes.ToString() + " minute";

    result += minutes > 1 ? "s" : "";

  }

  if (seconds < 60 && seconds > 0){

      if(result.Length > 0)

      {

          result += " and ";

      }

    result +=  seconds.ToString() + " second";

    result += seconds > 1 ? "s" : "";

  }

  return result;

}       

}

}