import sys
input = sys.stdin.readline

class BIT:
	def __init__(self, N):
		self.N = N
		self.bit = [0] * (N + 1)
		self.b = 1 << N.bit_length() - 1

	def add(self, a, w):
		x = a + 1
		while(x <= self.N):
			self.bit[x] += w
			x += x & -x

	def sum(self, a):
		ret, x = 0, a
		while(x > 0):
			ret += self.bit[x]
			x -= x & -x
		return ret

	def rsum(self, l, r):
		return self.sum(r) - self.sum(l)

"""
Main Code
"""

n = int(input())
a = map(int, input().split())

bt = BIT(n)
rev = 0
for i, k in enumerate(a):
	bt.add(k, 1)
	rev += i - bt.sum(k)

if(rev & 1):
	print(-1)
else:
	print(1)