n = int(input())
x = list(map(int, input().split()))
t = 0
for i in range(n):
    t |= 1 << x[i]
def loop(i, acc):
    def check(o):
        return (t & (1 << ((i + o) % 12))) == 0
    if i == 12:
        return acc
    if check(1) and check(3) and check(6) and check(8) and check(10):
        acc.append(i)
    return loop(i + 1, acc)
res = loop(0, [])
if len(res) == 1:
    print(res[0])
else:
    print(-1)