#include <bits/stdc++.h>

using namespace std;

#define rep(i,n) for(int i = 0; i < (int)(n); ++i)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; --i)
#define ALL(a) a.begin(), a.end()
#define Sort(a) sort(a.begin(), a.end())
#define RSort(a) sort(a.rbegin(), a.rend())

typedef long long int ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef vector<char> vc;
typedef vector<string> vst;
typedef vector<double> vd;
typedef pair<long long, long long> P;

const long long INF = 0x1fffffffffffffff;
const long long MOD = 1000000007;
const long double PI = acos(-1);
 
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T, class U> inline T vin(T& vec, U n) { vec.resize(n); for(int i = 0; i < (int) n; ++i) cin >> vec[i]; return vec; }
template<class T> inline void vout(T vec, string s = "\n"){ for(auto x : vec) cout << x << s; }
template<class... T> void in(T&... a){ (cin >> ... >> a); }
void out(){ cout << '\n'; }
template<class T, class... Ts> void out(const T& a, const Ts&... b){ cout << a; (cout << ... << (cout << ' ', b)); cout << '\n'; }
template<class T, class U> void inGraph(vector<vector<T>>& G, U n, U m, bool directed = false){ G.resize(n); for(int i = 0; i < m; i++){ int a, b; cin >> a >> b; a--, b--; G[a].push_back(b); if(!directed) G[b].push_back(a); } }

ll n;
vll s;

template <typename T>
struct binary_indexed_tree{
    int N;
    vector<T> BIT;
    binary_indexed_tree(int N): N(N), BIT(N + 1, 0){
    }
 
    void add(int i, T x){
        i++;
        while(i <= N){
            BIT[i] += x;
            i += i & -i;
        }
    }
 
    T sum(int i){
        T ans = 0;
        while(i > 0){
            ans += BIT[i];
            i -= i & -i;
        }
        return ans;
    }
 
    T sum(int L, int R){
        return sum(R) - sum(L);
    }
 
    int lower_bound(T x){
        if(x <= 0){
            return 0;
        }else{
            int v = 0, r = 1;
            while(r < N) r = r << 1;
            for(int len = r; len > 0; len = len >> 1){
                if(v + len < N && BIT[v + len] < x){
                    x -= BIT[v + len];
                    v += len;
                }
            }
            return v;
        }
    }
 
    int upper_bound(T x){
        if(x < 0){
            return 0;
        }else{
            int v = 0, r = 1;
            while(r <= N) r = r << 1;
            for(int len = r; len > 0; len = len >> 1){
                if(v + len <= N && BIT[v + len] <= x){
                    x -= BIT[v + len];
                    v += len;
                }
            }
            return v;
        }
    }
};

void input(){
    in(n);
    vin(s, n);
}
 
void solve(){
    ll res = 0;
    binary_indexed_tree<ll> BIT(n + 1);
    rep(i, n){
        res += BIT.sum(s[i], n + 1);
        BIT.add(s[i], 1);
    }
    if(res % 2 == 0){
        out(1);
    }else{
        out(-1);
    }
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    input();
    solve();
}