/**
 * This program computes the factorial of a number.
 */
public class Factorial {
    public static void main(String[] args) {
	int input = Integer.parseInt(args[0]);
	double result = factorial(input);
	System.out.println(result);
    }
    
    public static double factorial(int x) {
	if (x<0)
	    return 0.0;
	double fact = 1.0;
	while (x>1) {
	    fact = fact * x;
	    x = x - 1;
	}
	return fact;
    }
}