// Problem: No.2089 置換の符号
// Contest: yukicoder
// URL: https://yukicoder.me/problems/no/2089
// Memory Limit: 512 MB
// Time Limit: 2000 ms

#include <bits/stdc++.h>

#define fastio ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
#define dbg(x) cout << #x << " = " << (x) << "\n";
#define popcount(x) __builtin_popcountll((x))
#define all(v) (v).begin(), (v).end()
#define pb emplace_back
#define x first
#define y second

using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;

const int inf = 0x3f3f3f3f;
const int mod = 1e9 + 7;

const int N = 10010;
struct BIT {
  int sz;
  vector<int> bit;
  BIT(int _n) {
    sz = _n;
    bit = vector<int>(sz + 1, 0);
  }
  int lowbit(int x) { return x & -x; }
  void add(int x, ll v) {
    for (int i = x; i <= sz; i += lowbit(i)) {
      bit[i] += v;
    }
  }
  ll ask(int x) {
    ll ret = 0;
    for (int i = x; i >= 1; i -= lowbit(i)) {
      ret += bit[i];
    }
    return ret;
  }
};

void solve() {
  int n;
  cin >> n;
  BIT bit(N);
  int ans = 0;
  int x;
  for (int i = 1; i <= n; i++) {
    cin >> x;
    ans += i - 1 - bit.ask(x);
    bit.add(x, 1);
  }
  if (ans & 1)
    cout << "-1\n";
  else
    cout << "1\n";
}

int main() {
  fastio;
  int t = 1;
  // cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}