#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <tuple>
#include <deque>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
typedef pair<int, double> Pid;
typedef pair<double, int> Pdi;
typedef pair<ll, int> Pl;
typedef pair<int, pair<int, int>> PP;
const double PI = 3.1415926535897932;   // acos(-1)
const double EPS = 1e-15;
const ll mod = 1e+9 + 7;
const int INF = 1001001001;

#define chmax(x, y) x = max(x, y)
#define chmin(x, y) x = min(x, y)
#define chadd(x, y) x = (x + y) % mod

template<typename Monoid>
struct SegmentTree{
    using F = function<Monoid(Monoid, Monoid)>;

    int sz;
    vector<Monoid> seg;

    const F f;      // モノイドに対して二項演算を行う関数オブジェクト
    const Monoid M1;

    SegmentTree(int n, const F f, const Monoid &M1) : f(f), M1(M1){
        sz = 1;
        while(sz < n)   sz <<= 1;
        seg.assign(2 * sz, M1);
    }

    void set(int k, const Monoid &x){
        seg[k + sz] = x;
    }

    void build(){
        for(int k = sz - 1; k > 0; --k){
            seg[k] = f(seg[k << 1], seg[k << 1 | 1]);
        }
    }

    void update(int k, const Monoid &x){
        k += sz;
        seg[k] = x;
        while(k >>= 1){
            seg[k] = f(seg[k << 1], seg[k << 1 | 1]);
        }
    }

    Monoid query(int a, int b){
        Monoid L = M1, R = M1;
        for(a += sz, b += sz; a < b; a >>= 1, b >>= 1){
            if(a & 1)   L = f(L, seg[a++]);
            if(b & 1)   R = f(seg[--b], R);
        }
        return f(L, R);
    }

    Monoid operator[](const int &k) const{
        return seg[k + sz];
    }
};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    string s;
    cin >> s;
    int n = s.length();
    vector<vector<int>> pos(26);
    for(int i = 0; i < n; ++i){
        int id = s[i] - 'a';
        pos[id].push_back(i);
    }
    int oddcnt = 0, evencnt = 0;
    for(int i = 0; i < 26; ++i){
        if(pos[i].size() == 0)  continue;
        if(pos[i].size() % 2 == 0)  ++evencnt;
        else    ++oddcnt;
    }
    if(n % 2 == 0 && oddcnt > 0){
        cout << -1 << endl;
        return 0;
    }
    if(n % 2 != 0 && oddcnt != 1){
        cout << -1 << endl;
        return 0;
    }

    vector<P> left, middle;         // (pos, char)
    vector<vector<int>> right(26);  // (char, pos)
    for(int i = 0; i < 26; ++i){
        int sz = pos[i].size();
        if(sz == 0) continue;

        if(sz % 2 == 0){
            for(int j = 0; j < sz / 2; ++j) left.push_back(P(pos[i][j], i));
            for(int j = sz / 2; j < sz; ++j)    right[i].push_back(pos[i][j]);
        }
        else{
            for(int j = 0; j < sz / 2; ++j) left.push_back(P(pos[i][j], i));
            middle.push_back(P(pos[i][sz / 2], i));
            for(int j = sz / 2 + 1; j < sz; ++j)   right[i].push_back(pos[i][j]);
        }
        sort(right[i].begin(), right[i].end());
    }
    sort(left.begin(), left.end());

    vector<int> next(26, 0);    // right において、次はどの index であるかを表す
    vector<P> p(n);
    priority_queue<P> que;
    for(int i = 0; i < left.size(); ++i){
        p[i] = left[i];
        que.push(P(p[i].first, i));
    }
    if(n % 2 == 0){
        for(int i = n / 2; i > 0; --i){
            int char_id = p[i - 1].second;
            p[n - i] = P(right[char_id][next[char_id]++], char_id);
            que.push(P(p[n - i].first, n - i));
        }
    }
    else{   // n % 2 != 0
        p[n / 2] = middle[0];
        que.push(P(p[n / 2].first, n / 2));
        for(int i = n / 2; i > 0; --i){
            int char_id = p[i - 1].second;
            p[n - i] = P(right[char_id][next[char_id]++], char_id);
            que.push(P(p[n - i].first, n - i));
        }
    }

    SegmentTree<int> inversion(n, [](int a, int b){return a + b;}, 0);
    ll res = 0;
    while(!que.empty()){
        P hoge = que.top();
        que.pop();

        int val = hoge.first, id = hoge.second;
        inversion.update(id, 1);
        res += inversion.query(0, id);
    }
    cout << res << endl;
}

Measured memory_bytes: 8968