using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var data = "/Date(1638556214680-0300)/";

        var alexData = Program.AlexDataDeString(data);

        var dataCorreta = Program.DataDeString(data);

        Console.WriteLine("Alex data: " + alexData);

        Console.WriteLine("data correta: " + dataCorreta);

    }

    public static DateTime? DataDeString(string DHIniciado)

    {

        var dhRegex = new Regex(@"(-?\d+)([+-]{1})(\d{2})(\d{2})");

        var dhMatch = dhRegex.Match(DHIniciado);

        if (!dhMatch.Success)

            return null;

        var unixTime = Convert.ToInt64(dhMatch.Groups[1].Value);

        var offsetSignal = dhMatch.Groups[2].Value;

        var offsetHours = Convert.ToInt32(dhMatch.Groups[3].Value);

        var offsetMinutes = Convert.ToInt32(dhMatch.Groups[4].Value);

        if (offsetSignal == "-")

        {

            offsetHours = 0 - offsetHours;

            offsetMinutes = 0 - offsetMinutes;

        }

        var data = new DateTime(1970, 1, 1);

        data = data.AddMilliseconds(unixTime);

        data = data.AddHours(offsetHours);

        data = data.AddMinutes(offsetMinutes);

        return data;

    }

    public static DateTime AlexDataDeString(string DHIniciado)

    {

        DHIniciado = DHIniciado.Replace(@"/Date(","");

        DHIniciado = DHIniciado.Replace(@"-0000)/","");

        DHIniciado = DHIniciado.Replace(@"-0100)/","");

        DHIniciado = DHIniciado.Replace(@"-0200)/","");

        DHIniciado = DHIniciado.Replace(@"-0300)/","");

        DHIniciado = DHIniciado.Replace(@"/","");

        DHIniciado = DHIniciado.Replace(@"-","");

        DHIniciado = DHIniciado.Replace(@"(","");

        DHIniciado = DHIniciado.Replace(@")","");

        DHIniciado = DHIniciado.Replace(@" ","");

        Console.WriteLine(DHIniciado);

        DateTime dotNetDate = new DateTime(1970, 1, 1);

        dotNetDate = dotNetDate.AddMilliseconds(Convert.ToInt64(DHIniciado));

        return dotNetDate;

    }

}