N = int(input())
S = list(map(lambda x: int(x)-1, input().split()))

xs = S[:]
cnt = 0
for i in range(N):
    if xs[i] == i: continue
    x = xs[i]
    xs[i], xs[x] = xs[x], xs[i]
    cnt += 1

if cnt % 2 == 0:
    print(1)
else:
    print(-1)