#include <bits/stdc++.h>
using namespace std;
template <typename T>
class fenwick {
public:
vector<T> fenw;
int n;
fenwick(int _n) : n(_n) {
fenw.resize(n);
}
void modify(int x, T v) {
while (x < n) {
fenw[x] += v;
x |= (x + 1);
}
}
T get(int x) {
T v{};
while (x >= 0) {
v += fenw[x];
x = (x & (x + 1)) - 1;
}
return v;
}
};
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
int n;
cin >> n;
string s;
cin >> s;
n = 2 * n;
vector<vector<int>> pos(26);
for (int i = 0; i < n; i++) {
pos[s[i] - 'a'].push_back(i);
}
vector<int> cnt(26);
for (int i = 0; i < 26; i++) {
cnt[i] = (int) pos[i].size() / 2;
}
string t = "";
for (int i = 0; i < n; i++) {
int c = s[i] - 'a';
if (cnt[c] > 0) {
t += s[i];
cnt[c] -= 1;
}
}
t = t + t;
vector<int> a;
vector<int> nxt(26);
for (int i = 0; i < n; i++) {
int c = t[i] - 'a';
a.push_back(pos[c][nxt[c]]);
nxt[c] += 1;
}
long long ans = 0;
fenwick<int> fenw(n);
for (int i = 0; i < n; i++) {
ans += i - fenw.get(a[i]);
fenw.modify(a[i], 1);
}
cout << ans << '\n';
return 0;
}
