class Factorial{
	static long method(int n) throws ArgumentException{
		long s=1;
		if (n>=0){
			if (n>=0){
				for(int i=2;i<=n;i++){
					s=s*i;
				}
			}
		}else{
			throw new ArgumentException(n);
		}
		return s;
	}
	public static void main(String[] args){
		try{
			System.out.println("n! = " +method(-1));
		}catch (ArgumentException e){
			System.out.println(e);
		}
	}
}

class ArgumentException extends Exception{
	private int n;
	ArgumentException(){
	}
	
	ArgumentException(int n){
		this.n=n;
	}
	public String toString(){
		return ("Exception["+n+"]");
	}
}