      private void Unchecked_Click(object sender, EventArgs e)
        {
            int n1 = Convert.ToInt32(textBox1.Text);
            int n2 = Convert.ToInt32(textBox2.Text);
            int n3 = unchecked(n1 * n2);
            label3.Text = "Result is " + n3.ToString();
       
        }
