import sys
input = sys.stdin.readline
from collections import *

class BIT:
    def __init__(self, n):
        self.n = n
        self.bit = [0]*(n+1)
    
    def add(self, i, x):
        i += 1
        
        while i<=self.n:
            self.bit[i] += x
            i += i&(-i)

    def acc(self, i):
        s = 0
        
        while i>0:
            s += self.bit[i]
            i -= i&(-i)
        
        return s

N = int(input())
S = list(map(int, input().split()))
bit = BIT(N)
inv = 0

for i in range(N):
    inv += i-bit.acc(S[i])
    bit.add(S[i]-1, 1)

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