#include<iostream>
#include <map>
#include <vector>
//#include<bits/stdc++.h>
using namespace std;
const int INF = 1e8;
void swap_characters(int S, int E, string & str) {
    if(S < E) {
        char c = str[S];
        for(int i = S; i < E; i++) {
            str[i] = str[i + 1];
        }
        str[E] = c;
    }
    else {
        char c = str[S];
        for(int i = S; i > E; i--) {
            str[i] = str[i - 1];
        }
        str[E] = c;
    }

}
int main() {
    ios_base::sync_with_stdio(false);
    int n;
    cin >> n;
    string s;
    cin >> s;

    vector<int> cnt(26, 0);

    for(int i = 0; i < n; i++) {
        cnt[s[i] - 'a']++;
    }
    int odd = 0;
    for(int i = 0; i < 26; i++) {
        if(cnt[i] % 2 == 1) {
            odd++;
        }
    }
    if(odd > 1) {
        cout << "GRESHKA" << endl;
        return 0;
    }
    int res = 0;
    for(int i = 0; i < n / 2; i++) {
        if(s[i] != s[n - i - 1]) {
            int E = INF;
            int S = -INF;
            for(int j = i + 1; j < n - i - 1; j++) {
                if(s[j] == s[n - i - 1]) {
                    E = j;
                    break;
                }
            }
            for(int j = n - i - 2; j > i; j--) {
                if(s[j] == s[i]) {
                    S = j;
                    break;
                }
            }
            if(E - i < n - i - 1 - S) {

                swap_characters(E, i, s);
                res += E - i;
            }
            else {
                swap_characters(S, n - i - 1, s);
                res += n - i - 1 - S;
            }
        }
    }

    cout << res << endl;
    return 0;
}