///////    Factn.java    ///////

class Factn
{
    public static int factorial(int n)
    {  int ans = 1;
       while (n > 1)
       {    ans = ans * n;       
            n = n - 1;
       } 
       return ans;
    }

/** Usage: java Factorial n
           where n is a non-negative interger
           displays n!
*/
    public static void main(String[] args)
    {   if ( args.length != 1 )
           System.err.println("Usage: Factorial n");
     // converts string to int
        int n = Integer.valueOf(args[0]).intValue();
        if ( n >= 0 )
           System.out.println(factorial(n));
        else
           System.err.println("Factorial("+ n +")?");
    }
}