N=int(input())
A=list(map(int,input().split()))

B=[A[0]]
a=A[0]
for x in A[1:]:
    if a!=x:
        a=x
        B.append(a)


if len(B)==len(set(B)):
    print(0)
elif B[0]==B[-1]:
    print(1)
else:
    print(-1)