static void Main()
{
     Task<int> primeNumberTask = Task.Run(() =>
     {
          Thread.Sleep(3000);
          return 34;
     });

     primeNumberTask.ContinueWith(antecedent =>
     {
          int result = antecedent.Result;
          Console.WriteLine(result); // zapis 34
     });

     Console.ReadKey();
}