private void button4_Click(object sender, EventArgs e)
        {
            string username;
            string password;

            username = textBox1.Text;
            password = textBox2.Text;
            if (username == "admin" && password == "admin")
            {
                Koordinator_Login koordinator = new Koordinator_Login();
                label5.Visible = false;
                this.Hide(); koordinator.Show();
            }
            else
            {
                label5.Visible = true;
            }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            Koordinator_Login koordinator = new Koordinator_Login();

            this.Close();    koordinator.Show();
        }