from sys import stdin


def main():
    input = lambda: stdin.readline()[:-1]
    N = int(input())
    T = list(map(int, input().split()))

    ans = []
    for d in range(12):
        key = []
        for a in (d, d + 2, d + 4, d + 5, d + 7, d + 9, d + 11):
            key.append(a % 12)
        for t in T:
            if t not in key:
                break
        else:
            ans.append(d)
    if len(ans) == 1:
        print(*ans)
    else:
        print(-1)


main()