private int jc(int x)
{
   if(x=1)return 1;
   else return jc(x-1)*x;
}

        static int factorial(int x)
        {
            if (x == 1)
                return 1;
            else
                return factorial(x - 1) * x;
        }

namespace Program
class Program
{
   public static void Main()
   {
     int x=9;
     System.Console.WriteLine(jc(x));
   }
  ...
}