class Program
    {
        static void Main(string[] args)
        {
            aa a = new aa();
            a.ff = 19;
        }
    }
    public class aa
    {
        int f1;
        public int ff
        {
            set
            {
                System.Console.WriteLine("in set " + value);
                f1 = value;
            }
        }
    }

what is the accurate solution of its?