public static void RunSync(Func<Task> fn) => Task.Run(fn).ConfigureAwait(false).GetAwaiter().GetResult();
public static T RunSync<T>(Func<Task<T>> fn) => Task.Run(fn).ConfigureAwait(false).GetAwaiter().GetResult();

// an async main:
static void Main(string[] args)
{
     var result = RunSync(() => MainAsync());
     Console.ReadKey();
}