using System;

public class Program

{

    public static void Main()

    {

        var start = DateTime.Parse("01.01.1900");

        Console.WriteLine($"start of time \t{start}");

        var daysStr = "44443.8340277778";

        var days = double.Parse(daysStr);

        Console.WriteLine($"days elapsed \t{days}");

        var date = start.AddDays(days);

        Console.WriteLine($"new date is \t{date}");

    }

}