import sys
input = sys.stdin.readline

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

for i in range(N):
    S[i]-=1

S_INV=[-1]*N

for i in range(N):
    S_INV[S[i]]=i

ANS=0

for i in range(N):
    if S[i]!=i:
        x=S_INV[i]
        ANS+=1

        S[x],S[i]=S[i],S[x]

        S_INV[S[x]]=x
        S_INV[S[i]]=i
       
if ANS%2==0:
    print(1)
else:
    print(-1)