#include <bits/stdc++.h>
#define _GLIBCXX_DEBUG
using namespace std;
using ll = long long;
using ld = long double;
using V = vector<int>;
using Vll = vector<ll>;
using Vld = vector<ld>;
using Vbo = vector<bool>;
using VV = vector<V>;
using VVll = vector<Vll>;
using VVld = vector<Vld>;
using VVbo = vector<Vbo>;
using VVV = vector<VV>;
using VVVll = vector<VVll>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using Pld = pair<ld, ld>;
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define rep(i, n) rep2(i, 0, n)
#define drep(i, n) drep2(i, n, 0)
#define all(a) (a).begin(), (a).end()
struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
template<typename T> inline int sz(T &x) { return x.size(); }
template<typename T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }
template<typename T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p) { is >> p.first >> p.second; return is; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p) { os << '(' << p.first << ", " << p.second << ')'; return os; }
template<typename T> istream &operator>>(istream &is, vector<T> &v) { for (auto &e : v) is >> e; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &v) { for (auto &e : v) os << e << ' '; return os; }
template<typename T> inline int count_between(vector<T> &a, T l, T r) { return lower_bound(all(a), r) - lower_bound(all(a), l); } // [l, r)
inline int fLog2(const int x) { assert(x > 0); return 31-__builtin_clz(x); } // floor(log2(x))
inline int fLog2(const ll x) { assert(x > 0); return 63-__builtin_clzll(x); }
inline int cLog2(const int x) { assert(x > 0); return (x == 1) ? 0 : 32-__builtin_clz(x-1); } // ceil(log2(x))
inline int cLog2(const ll x) { assert(x > 0); return (x == 1) ? 0 : 64-__builtin_clzll(x-1); }
inline int popcount(const int x) { return __builtin_popcount(x); }
inline int popcount(const ll x) { return __builtin_popcountll(x); }
void fail() { puts("-1"); exit(0); }
const int INF  = 1<<30;
const ll INFll = 1ll<<62;
const ld EPS   = 1e-10;
const ld PI    = acos(-1.0);
// const int MOD  = int(1e9)+7;
// const int MOD  = 998244353;


template<typename T>
struct FenwickTree {
  int n; vector<T> d;
  FenwickTree(int n = 0) : n(n), d(n+1) {}
  void add(int i, T a = 1) { for (++i; i <= n; i += i & -i) d[i] += a; }
  T _sum(int i) { T x = 0; for (; i > 0; i -= i & -i) x += d[i]; return x; }
  T sum(int l, int r) { return _sum(r) - _sum(l); } // [l, r)
  T operator[](const int i) { return sum(i, i+1); }
};


const int M = 26;

int main() {
  string s; cin >> s;
  int n = sz(s);

  FenwickTree<int> ft(n);
  rep(i, n) ft.add(i);

  vector<deque<int>> pos(M);
  rep(i, n) pos[s[i] - 'a'].push_back(i);

  int cnt = 0;
  rep(i, M) if (sz(pos[i])&1) ++cnt;
  if (cnt > 1) fail();

  int k = n/2;
  ll ans = 0;

  rep(i, k) {
    int j = -1;
    int cmin = INF;
    rep(l, M) {
      if (sz(pos[l]) <= 1) continue;
      int now = 0;
      now += ft.sum(0, pos[l].front());
      now += ft.sum(pos[l].back()+1, n);
      if (chmin(cmin, now)) j = l;
    }
    ans += cmin;
    ft.add(pos[j].front(), -1);
    ft.add(pos[j].back(), -1);
    pos[j].pop_front();
    pos[j].pop_back();
  }

  cout << ans << '\n';
  return 0;
}


Measured memory_bytes: 5392