using System;

using System.Threading.Tasks;

using System.Threading;

using System.Collections.Generic;

public class Program

{

    public async void Main()

    {

        Console.WriteLine("Hello World");

        var T1 = Sum(2,5);

        var T2 = Sum(T1.Result, 7);

        var T3 = Sum(T2.Result, 7);

        var myVar = T3.Result;

        var listOfTasks = new List<Task>{T1,T2,T3};

        await Task.WhenAll(listOfTasks);

        Console.Write(myVar);

    }

    public async Task<int> Sum(int num1, int num2){

        return await Task.Factory.StartNew(() => {

            Thread.Sleep(1000);

            return num1 + num2;

        });

    }

}