BNY

/*
Author: Mehul Chaturvedi
*/

#include <bits/stdc++.h>
using namespace std;
using ll = long long;


ll findMinimumAdjacentSwaps(vector<ll> &arr, ll N) {
    bool visited[N + 1];

    ll minimumSwaps = 0;
    memset(visited, false, sizeof(visited));

    for (int i = 0; i < N; i++) {
        if (visited[i]) continue;
        visited[i] = 1;
        ll count = 0;
        bool flag = 0;
        for (int j = i + 1; j < N; ++j) {
            if (visited[j]) continue;
            if (arr[j] == arr[i]) {
                visited[j] = 1;
                minimumSwaps += count;
                flag = 1;
                break;
            } else {
                count++;
            }
        }

        if (!flag) {
            visited[N - 1] = 1;
            minimumSwaps += count;
        }
    }

    return minimumSwaps;
}


void solve() {
    ll n; cin >> n;

    vector<ll> a;
    a.resize(n);

    map<ll, ll> freq;
    for (ll i = 0; i < n; ++i) {
        cin >> a[i];
        freq[a[i]]++;
    }

    ll notEvenFreq = 0;
    ll k = 0;
    map<ll, ll> m;
    for (auto &elem : freq) {
        if (elem.second % 2 != 0) notEvenFreq++;
        m[elem.first] = k++;
    }

    if (notEvenFreq > n % 2) {
        cout << -1 << '\n';
        return;
    }

    for (ll i = 0; i < a.size(); ++i) {
        a[i] = m[a[i]];
    }

    ll ans = findMinimumAdjacentSwaps(a, n);

    cout << ans << '\n';
    return;
}

int main(int argc , char ** argv) {
    ios_base::sync_with_stdio(false) ;
    cin.tie(NULL) ;

    ll t = 1;
    while (t--) {
        solve();
    }

    return 0 ;
}