using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static void Main()

    {

        CancellationTokenSource ct = new CancellationTokenSource();

        ct.CancelAfter(3500);

        CancellationToken tok = ct.Token;

        int val = 0;

        {

            Task t = Task.Run( () =>

                       val = fun(), tok

                      );

        t.Wait(tok);

        }

​

    Console.WriteLine(val);

    }

    public static int fun()

    {

        Thread.Sleep(4000);

        return 10;

    }

}