close all open forms that formBorderStyle is None

Hi

I wanna close all of the open forms but their BorderStyle property is None so the below code don't work for this issue. which code should I use instead?!

foreach (Form f in Application.OpenForms)
            {
                if (f.Name != "frmMain")
                {
                    f.Close();
                    break;
                }
            }

---

امیدوارم همیشه بروز باشید I hope always be up2date