public class Factorial{
    static int factorial(int n){
        int return_val;
        Trace.reverseIndent(n,
            "entering factorial("+n+")");
        if (n<0)
            throw new IllegalArgumentException("factorial("+n+") undefined");
        if (n<=1)
            return_val=1;
        else
            return_val=n*factorial(n-1);
        Trace.reverseIndent(n,
            "factorial(" +n+")="+ return_val);
        return return_val;
    }
    public static void main(String [] args){
        System.out.println(factorial(6));
    }

}
//