using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        var message = "990105 2347";

        var span = message.AsSpan();

        var builder = new StringBuilder();

        builder

            .Append(span.Slice(0,2))

            .Append(' ')

            .Append(span.Slice(2,2))

            .Append(' ')

            .Append(span.Slice(4,2))

            .Append(' ')

            .Append(span.Slice(7,2))

            .Append(':')

            .Append(span.Slice(9,2));

        Console.WriteLine(builder.ToString());

    }

}