private void buttonCap_Click(object sender, EventArgs e)
        {
            double  f0, L, C, H,result;
            const double conpi = 3.1415926;
            f0 = double.Parse(textBoxF.Text);
            L = double.Parse(textBoxL.Text);
            H=f0*f0*L;
            result = 4 * (conpi *conpi) * H;
            C = 1 / result;
            textBoxC.Text = C.ToString();
        }