using System;

using System.Threading.Tasks;

​

public class Program

{

    public abstract class BaseClass

    {

        public abstract Task MetodoAssincrono();

        public abstract Task<int> MetodoAssincronoComRetorno();

    }

​

    public class DerivedClass : BaseClass

    {

        public override async Task MetodoAssincrono()

        {

            Console.WriteLine("MetodoAssincrono");

            await Task.CompletedTask;

        }

​

        public override async Task<int> MetodoAssincronoComRetorno()

        {

            Console.WriteLine("MetodoAssincronoComRetorno");

            return await Task.FromResult<int>(5);

        }

    }

​

    public static void Main()

    {

        var c = new DerivedClass();

        c.MetodoAssincrono().Wait();

        Console.WriteLine(c.MetodoAssincronoComRetorno().Result);

    }

}