#include <bits/stdc++.h>
using namespace std;
#define int long long
const int MAXN = 2e5 + 25;
struct bit {
int tree[MAXN] = {};
void add (int x) {
if (x < 0 || x > MAXN) return;
for (; x < MAXN; x += x & (-x)) tree[x]++;
}
int get (int x) {
if (x < 0 || x > MAXN) return 0;
int sum = 0; for (; x; x -= x & (-x)) sum += tree[x];
return sum;
}
} cur;
int n;
string s;
vector <int> occ[26];
int pref[MAXN];
signed main () {
ios::sync_with_stdio(0);
cin.tie(0); memset(cur.tree, 0, sizeof(cur.tree));
cin >> n >> s;
s.insert(s.begin(), '0');
for (int i = 1; i <= 2 * n; i++) occ[s[i] - 'a'].push_back(i);
vector <pair <int, int>> ll2;
for (int i = 0; i < 26; i++) {
if (occ[i].empty()) continue;
for (int j = (int)occ[i].size() / 2; j < (int)occ[i].size(); j++) {
ll2.push_back({occ[i][j - (int)occ[i].size() / 2], occ[i][j]});
pref[occ[i][j]]++;
}
}
sort(ll2.begin(), ll2.end()); ll2.insert(ll2.begin(), {0, 0});
for (int i = 1; i <= 2 * n; i++) pref[i] += pref[i - 1];
int sum = 0; int sum2 = 0; for (int i = 1; i <= n; i++) {
sum += pref[ll2[i].first];
sum2 += cur.get(ll2[i].second);
cur.add(ll2[i].second);
}
cout << sum + n * (n - 1) / 2 - sum2 << '\n';
}
