Write a c# code to find the factorial of a function?

static int GetFactorial(string inputValue)
{
int number;
bool IsNumber = true;
IsNumber = Int32.TryParse(inputValue, out number);
if (IsNumber)
{
int result = 1;
int counter = number;
do
{
result = result * counter;
counter--;
} while (counter >= 1);
return result;
//with factorial
//if (number <= 1)
//{
// return 1;
//}
//else
//{
// result = number * GetFactorial((number - 1).ToString());
// return result;
//}
}
else
{
throw new Exception("Input value is not a valid number");
}
}