Add solution for Challenge 18 by mick4711 #27

Job	Run time
Validate Submission Security	6s
test-submissions (challenge-3)	19s
test-submissions (challenge-5)	13s
test-submissions (challenge-2)	21s
test-submissions (challenge-4)	12s
test-submissions (challenge-7)	14s
test-submissions (challenge-1)	25s
test-submissions (challenge-8)	13s
test-submissions (challenge-10)	13s
test-submissions (challenge-6)	16s
test-submissions (challenge-14)	11s
test-submissions (challenge-12)	14s
test-submissions (challenge-9)	11s
test-submissions (challenge-15)	12s
test-submissions (challenge-22)	11s
test-submissions (challenge-19)	13s
test-submissions (challenge-16)	13s
test-submissions (challenge-17)	13s
test-submissions (challenge-13)	14s
test-submissions (challenge-21)	13s
test-submissions (challenge-18)	23s
test-submissions (challenge-11)	10s
test-submissions (challenge-20)	14s
test-submissions (challenge-24)	14s
test-submissions (challenge-26)	12s
test-submissions (challenge-27)	13s
test-submissions (challenge-23)	11s
test-submissions (challenge-30)	14s
test-submissions (challenge-29)	12s
test-submissions (challenge-28)	13s
test-submissions (challenge-25)	13s
	7m 6s

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