static void Main(string[] args)
    {
        var watch = new Stopwatch();
        watch.Start();

        var result = GetStringAsync();

        var time = watch.ElapsedMilliseconds;
    }

    static async Task<string> GetStringAsync()
    {
        var result = "";
        result += await H1();
        result += await H2();
        result += await H3();

        return result;

    }

    static async Task<string> H1()
    {
        Console.WriteLine("entered h1");
        Thread.Sleep(10000);
        return "1";
    }

    static async Task<string> H2()
    {
        Console.WriteLine("entered h2");
        Thread.Sleep(10000);
        return "2";
    }

    static async Task<string> H3()
    {
        Console.WriteLine("entered h3");
        Thread.Sleep(10000);
        return "3";
    }