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

struct fen{
    vector<int>tree;
    fen(int N)
    {
        tree.resize(N+1);
    }

    ll somma(int i)
    {
        int sum=0;
        for(;i>0;i-=i&-i)
        {
            sum+=tree[i];
        } 
        return sum;
    }

    void agg(int i)
    {
        for(;i<tree.size();i+=i&-i)
        {
            tree[i]++;
        }
    }


};


long long int paletta_sort(int N, int* V)
{
    vector<int>pari,disp;
    for(int i=0;i<N;i++)
    {
        if(V[i]%2==0&&i%2==0)pari.push_back(V[i]/2+1);
        else if(V[i]%2&&i%2)disp.push_back(V[i]/2+1);
        else return -1;
    }

    ll ris=0;

    fen pariTree(pari.size());
    for(int i=0;i<pari.size();i++)
    {
        ris+=i-pariTree.somma(pari[i]);
        pariTree.agg(pari[i]);
    }

    fen dispTree(disp.size());
    for(int i=0;i<disp.size();i++)
    {
        ris+=i-dispTree.somma(disp[i]);
        dispTree.agg(disp[i]);
    }
    return ris;
}