N,*T=map(int, open(0).read().split())
x=[0,2,4,5,7,9,11]
r=-1
for i in range(12):
	t = set((i+e)%12 for e in x)
	for e in T:
		if e not in t:
			break
	else:
		if r==-1:
			r=i
		else:
			print(-1)
			exit()
print(r)