private void button3_Click(object sender, EventArgs e)
{
    if (!this.textBox3.ReadOnly)
    {
        int length = this.textBox3.Text.Length;
        int num2 = 0;
        for (int i = 0; i < length; i++)
        {
            num2 += this.textBox1.Text[i];
            num2 *= i;
        }
        num2 /= 2;
        if (this.textBox4.Text == num2.ToString())
        {
            this.textBox6.ReadOnly = false;
        }
        else
        {
            MessageBox.Show("Wrong Password!", "Error");
        }
    }
}