from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline

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

def mergecount(A):
    cnt = 0
    n = len(A)
    if n>1:
        A1 = A[:n>>1]
        A2 = A[n>>1:]
        cnt += mergecount(A1)
        cnt += mergecount(A2)
        i1=0
        i2=0
        for i in range(n):
            if i2 == len(A2):
                A[i] = A1[i1]
                i1 += 1
            elif i1 == len(A1):
                A[i] = A2[i2]
                i2 += 1
            elif A1[i1] <= A2[i2]:
                A[i] = A1[i1]
                i1 += 1
            else:
                A[i] = A2[i2]
                i2 += 1
                cnt += n//2 - i1
    return cnt
if mergecount(S)%2:
    print(-1)
else:
    print(1)