public class Factorial {                       // Defines a class
   public static void main(String[] args) {    // The program starts here
   int input = Integer.parseInt(args[0]);      // Get the user's input
   double result = factorial(input);           // Computes the factorial
   System.out.println(result);                 // Prints down the result
   }                                           // The main() methods end here

   public static double factorial(int x) {     // This method computes x!!!
       if (x < 0)                              // Searches for wrong input
          return 0.0;                          // If the input is bad, return 0.0
       double fact = 1.0;                      // Begin with an initial value
       while(x > 1) {                          // Loops until x equals 1
          fact = fact * x;                     // Multiply by x each time
          x = x - 1;                           // And then decrement x
          }                                    // Jump back to the start of the loop
          return fact;                         // Return the result
       }                                       // factorial() ends here
   }