using System;

public class Program

{

    public static void Main()

    {

        var s = DateTime.Now.ToString("M/d HH:mm:ss"); // 4/28 8:00:00

        DateTime dt = new DateTime(100,1,1);

        var b = DateTime.TryParseExact(s, new string[] {"M/d HH:mm:ss", "MM/d HH:mm:ss","M/dd HH:mm:ss","MM/dd HH:mm:ss"}, System.Globalization.CultureInfo.InvariantCulture, 

System.Globalization.DateTimeStyles.None, out dt);

        Console.WriteLine(dt.ToString());

    }

}