n=int(input())
T=list(map(int,input().split()))
import collections
CT=collections.Counter(T)
l=[0,2,4,5,7,9,11]
ans=-1
for i in range(12):
    D=[]
    for i in l:
        D.append((i+1)%12)
    if not (CT-collections.Counter(D)):
        if ans==-1:
            ans=i
        else:
            exit(print(-1))

print(ans)