Calculate the Factorial of an Integer in C#

private void button1_Click(object sender, EventArgs e)
{
    int inputValue;
    if (int.TryParse(this.textBox1.Text, out inputValue) && inputValue > 0)
    {
        BigInteger bigInt = 1;
        while (inputValue > 1)
        {
            bigInt = BigInteger.Multiply(inputValue--, bigInt);
        }
        label1.Text = bigInt.ToString();
        label2.Text = bigInt.ToString().Length + " Digits";

    }
    else
    {
        label1.Text = "Invalid Input";
        label2.Text = "";
    }
}