class Bit:
  def __init__(self,n):
    self.size=n
    self.tree=[0]*(n+1)
  
  def sum(self, i):
    s=0
    while i>0:
      s+=self.tree[i]
      i-=i&-i
    return s
  
  def add(self,i,x):
    while i<=self.size:
      self.tree[i]+=x
      i+=i&-i

def inversion(a,flag=True):
  n=len(a)
  if flag:
    b=[(a[i],i+1) for i in range(n)]
    b.sort(key=lambda x:x[0])
    a=[i[1] for i in b]

  bit=Bit(n)
  cnt=0
  for i in range(n):
    bit.add(a[i],1)
    cnt+=i+1-bit.sum(a[i])
  return cnt

n=int(input())
a=list(map(lambda x:int(x)-1,input().split()))
if inversion(a)%2==0:
  print(1)
else:
  print(-1)