import collections
import itertools
N = int(input())
A = list(map(int,input().split()))
CA = collections.Counter(A)
va = len(CA)
GR = itertools.groupby(A+A)
L = []
for k,v in GR:
    L.append(len(list(v)))
AL = list(itertools.accumulate(L))+[0]
if AL[va-1]>=N:
    print(0)
else:
    for i in range(len(L)-va):
        if AL[i+va-1]-AL[i-1]>=N:
            print(1)
            exit()
    print(-1)