static void Main(string[] args)
{
if (args == null)
{
throw new ArgumentNullException(nameof(args));
}
var ibm = new IBM("International Bussness Machine", 12);
ibm.AttachInvestor(new Investor("Broker1"));
ibm.AttachInvestor(new Investor("Broker2"));
ibm.Price = 20;
ibm.Price = 100;
ibm.Price = 100;
Console.ReadKey();
}