n = int(input())
s = list(map(int,input().split()))
class BIT():
    def __init__(self,n,calc,mono):
        self.size = (1 << (n-1).bit_length()) + 1
        self.arr = [mono] * self.size
        self.calc = calc
        self.mono = mono
    
    def update(self,i,val):
        while i < self.size:
            self.arr[i] = self.calc([self.arr[i],val])
            i += -i & i
    
    def query(self,i):
        res = self.mono
        while i > 0:
            res = self.calc([res,self.arr[i]])
            i -= -i & i
        return res
bit = BIT(n+1,sum,0)
cnt = 0
for i in range(n):
    cnt += bit.query(s[-(i+1)])
    bit.update(s[-(i+1)]+1,1)
if cnt & 1:
    print(-1)
else:
    print(1)