/**
 * This program computes the factorial of a number
 */

public class Factorial {                   	// Define 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);      	// Compute the factorial
	System.out.println(result);            	// Print out the result
    }                                        	// The main() method ends here

    public static double factorial(int x) {  	// This method computes x!
	if (x < 0)                             	// Check for bad input
	    return 0.0;                        	//   if bad, return 0
	double fact = 1.0;                     	// Begin with an initial value
	while(x > 1) {                         	// Loop until x equals 1
	    fact = fact * x;                   	//   multiply by x each time
	    x = x - 1;                         	//   and then decrement x
	}                                      	// Jump back to the star of loop
	return fact;                           	// Return the result
    }                                        	// factorial() ends here
}                                          	// The class ends here