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

ll paletta_sort (int n, int a[]) {

  vector<ll> e, o;
  for (int i = 0; i < n; ++i) {
    if (i % 2 != a[i] % 2) return -1;

    if (i % 2) o.push_back(a[i]/2);
    else e.push_back(a[i]/2);
  }

  vector<ll> fen(e.size()+1);
  ll ans = 0;
  for (int i = n-1; i >= 0; i--) {
    for (int j = e[i]+1; j > 0; j -= j & -j) ans += fen[j];
    for (int j = e[i]+1; j < fen.size(); j += j & -j) fen[j]++;
  }

  fen.assign(o.size()+1, 0);
  for (int i = o.size()-1; i >= 0; i--) {
    for (int j = o[i]+1; j > 0; j -= j & -j) ans += fen[j];
    for (int j = o[i]+1; j < fen.size(); j += j & -j) fen[j]++;
  }

  return ans;
}

/*
int main() {

  ll n, k; cin >> n >> k;

  int a[n];
  for (int i = 0; i < n; ++i) cin >> a[i];

  cout << quadri(n, k, a) << '\n';
    
}
*/