Plugin for appointment

Question

Actually i tried in plug-in that concept. but it did not work.

this is the code which i used.Is there any mistake in this???

My need is when i create an appointment the values in location field should be copied to firstname of contact entity.

public void Execute(IPluginExecutionContext context)
    {
        DynamicEntity entity = null;

        if (context.InputParameters.Properties.Contains("Target") &&
            context.InputParameters.Properties["Target"] is DynamicEntity)
        {
            entity = (DynamicEntity)context.InputParameters.Properties["Target"];

            if (entity.Name != EntityName.appointment.ToString())
                return;
        }
        else
        {
            return;
        }
        try
        {
            Guid appointmentID = new Guid(context.OutputParameters["id"].ToString());

            ICrmService crmservice = context.CreateCrmService(true);

            appointment appObj = (appointment)crmservice.Retrieve(EntityName.appointment.ToString(), appointmentID, new ColumnSet(new string[] { "regardingobjectid", "location" }));
            if (appObj.regardingobjectid == null || appObj.regardingobjectid.type != "contact")
            {
                return;
            }
            Guid contactID = appObj.regardingobjectid.Value;

            contact cnt = new contact();
            cnt.contactid = new Key();
            cnt.contactid.Value = contactID;
            cnt.firstname = appObj.location;

            crmservice.Update(cnt);
        }
        catch (System.Web.Services.Protocols.SoapException ex)
        {
            throw new InvalidPluginExecutionException(
               "Invalid plug-in.", ex);
        }
    }