using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        var strDate = "20171130";

        DateTime dateValue;

        DateTime.TryParseExact(strDate, "yyyyMMdd", CultureInfo.InvariantCulture, DateTimeStyles.None, out dateValue);

        Console.WriteLine(dateValue.ToString("dd/MM/yyyy"));

    }

}