List<Student> studenci = new List<Student>();
        private void BN_DodajSer_Click(object sender, EventArgs e)
        {
            Student s = new Student();
            s.imie = TB_ImieSer.Text;
            studenci.Add(s);
            listBox1.Items.Add(s.imie);
        }

        private void BN_WczytajSer_Click(object sender, EventArgs e)
        {
            FileStream fsNew = new FileStream("student.dat", FileMode.Open);
            BinaryFormatter bfNew = new BinaryFormatter();
            List<Student> studenci = (List<Student>)bfNew.Deserialize(fsNew);
            //List<Student> studenci = bfNew.Deserialize(fsNew) as List<Student>;
            fsNew.Close();
            listBox1.Items.Clear();
         }

        private void BN_ZapiszSer_Click(object sender, EventArgs e)
        {
            FileStream fs = new FileStream("student.dat", FileMode.Create);
            BinaryFormatter bF = new BinaryFormatter();
            bF.Serialize(fs, studenci);
            fs.Close();
        }