using System;

using System.Globalization;                 

​

public class Program

{

    public static void Main()

    {

        //var d = new DateTime(2020, 2, 29);

        var d = Convert.ToDateTime("2020/02/29");

        Console.WriteLine("Date format (long):  {0}", d.ToString("yyyy-MM-dd hh:mm:ss", CultureInfo.InvariantCulture));

        var input= "2020/02/29";

        var test = Convert.ToDateTime((Convert.ToInt32(input.Substring(0, 4))).ToString() + input.Substring(4));

        Console.WriteLine("Date format (long):  {0}", test.ToString("yyyy-MM-dd hh:mm:ss", CultureInfo.InvariantCulture));

        Console.WriteLine(input.Substring(0, 4));

        Console.WriteLine(input.Substring(4));

        Console.WriteLine((Convert.ToInt32(input.Substring(0, 4))).ToString() + input.Substring(4));

    }

}