resource fact2()
	op factorial(val int a, res int result)
	op trick(val int a)


	for [ i = 0 to 20 ] {
	    call trick(i)
	}


	proc trick(a)  {
		int  ans
		factorial(a,ans)
		write(ans)
	}

	proc factorial(a,result)  {
		if (a <= 1) {
			result = 1
		} else {
			factorial(a-1,result)
			result = a * result
		}
	}
end