private void btnDeposit_Click(object sender, EventArgs e)
        {
            string amount = Interaction.InputBox("please, insert the amount what you could deposit.", "do a deposit");
            Users  user   = SUsers.getInstance();

            user.Bank.deposit(Convert.ToDouble(amount));
            cBank.updateBank(user.Bank);
            MessageBox.Show("cash added!!!", "successful operation");
            Principal_Load(sender, e);
        }