class BIT:
    def __init__(self, n):
        self.n = n; self.k = [0]*(n+1)
    def a(self, i, x):
        while i <= self.n: self.k[i] += x; i += i&-i
    def s(self, i):
        t = 0
        while i > 0: t += self.k[i]; i -= i&-i
        return t
bit = BIT(int(input())); x = 0
for i, v in enumerate(map(int, input().split())): x += i-bit.s(v); bit.a(v, 1)
print(-1 if x%2 else 1)