#include <bits/stdc++.h>
using namespace std;
struct fenwick
{
int n;
vector<int> bit;
fenwick() {}
fenwick(int n)
{
this->n = n + 5;
bit.resize(n + 5);
}
void add(int pos, int val)
{
while (pos < n)
{
bit[pos] += val;
pos += pos & -pos;
}
}
int get(int pos)
{
int ans = 0;
while (pos)
{
ans += bit[pos];
pos -= pos & -pos;
}
return ans;
}
int get(int l, int r)
{
return get(r) - get(l - 1);
}
int find(int k)
{
int sum = 0, pos = 0;
for (int i = __lg(n); i >= 0; i--)
{
if (pos + (1 << i) < n && sum + bit[pos + (1 << i)] < k)
{
sum += bit[pos + (1 << i)];
pos += (1 << i);
}
}
return pos + 1;
}
};
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
string s;
cin >> s;
string l = "", r = "";
int cnt[26]{};
for (char c : s) {
cnt[c - 'a']++;
}
for (int i = 0; i < 26; i++) {
cnt[i] >>= 1;
}
long long ans = 0;
for (char c : s) {
if (cnt[c - 'a']) {
cnt[c - 'a']--;
l += c;
ans += r.size();
}
else {
r += c;
}
}
deque<int> pl[26];
for (int i = 0; i < n; i++) {
pl[l[i] - 'a'].push_back(i);
}
vector<int> p(n);
for (int i = 0; i < n; i++) {
p[i] = pl[r[i] - 'a'][0];
pl[r[i] - 'a'].pop_front();
}
fenwick tree(n);
for (int i : p) {
i++;
ans += tree.get(i + 1, n);
tree.add(i, 1);
}
cout << ans;
return 0;
}
