1000DaysAfterBirth

using System;
using System.Globalization;

class ThousandDaysAfterBirth
{
    static void Main()
    {
        //Input must be in format dd-MM-yyyy (e.g 08-01-2017).
        string birthDate = Console.ReadLine();

        // Convert (parse) from string to DateTime (birthDate --> myDate).
        DateTime myDate = DateTime.ParseExact(birthDate, "dd-MM-yyyy", CultureInfo.InvariantCulture);

        //Add 999 days to myDate.
        DateTime after1000 = myDate.AddDays(999);

        //Convert from DateTime to string and format it like this: dd-MM-yyyy
        string after1000ToString = after1000.ToString("dd-MM-yyyy", CultureInfo.InvariantCulture);

        //Print 1000 days after birthDate.
        Console.WriteLine(after1000ToString);

        //*Not all cultures use the same format for dates. The "CultureInfo.InvariantCulture" property is neither a neutral nor a specific culture. It is a third type of culture that is culture-insensitive. The "CultureInfo.InvariantCulture" property is used if you are formatting a string (.ToString("dd-MM-yyyy")) or parsing a string (DateTime.Parse) that should be formattable / parseable by a piece of software independent of the user's local settings.
    }
}