#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx")
using std::abs;
using std::cerr;
using std::cin;
using std::cout;
using std::map;
using std::max;
using std::min;
using std::pair;
using std::set;
using std::string;
using std::swap;
using std::vector;
using ll = long long;
using uint = unsigned int;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using ull = unsigned long long;
template <typename T>
void _dbg(const char* _s, T _h) {
  cerr << _s << " = " << _h << "\n";
}
template <typename T, typename... Ts>
void _dbg(const char* _s, T _h, Ts... _t) {
  int _b = 0;
  while (((_b += *_s == '(') -= *_s == ')') != 0 || *_s != ',') cerr << *_s++;
  cerr << " = " << _h << ",";
  _dbg(_s + 1, _t...);
}
struct init {
  init() {
    cin.tie(0);
    std::iostream::sync_with_stdio(0);
    cout << std::fixed << std::setprecision(10);
    cerr << std::fixed << std::setprecision(5);
  }
  ~init() {}
} init;
const int MAXN = 111;
int32_t main() {
  int n;
  cin >> n;
  int a = 0, b = 0;
  for (int i = 0; i < n / 2; ++i) {
    int x;
    cin >> x;
    --x;
    a += abs(x - 2 * i);
    b += abs(x - (2 * i + 1));
  }
  cout << min(a, b) << '\n';
  return 0;
}
