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

long long paletta_sort(int N, int V[]) {
    vector<pair<int, int>> movements(N);
    for (int i{ }; i < N; ++i) movements[i] = { V[i], i };
    sort(movements.begin(), movements.end());

    long long tot{ };
    for (int i{ }; i < N; ++i) {
        int diff{ movements[i].first - movements[i].second };
        if (abs(diff) % 2 != 0) return -1;

        // For each num, the num of smaller nums on the right (only odds for odds and only evens for evens)
        for (int j{ i + 2 }; j < N; j += 2) {
            tot += V[j] < V[i];
        }
    }
    return tot;
}