#include <bits/stdc++.h>
using namespace std;
#define int long long
struct node {
int s, e, m, v;
node *l, *r;
node (int _s, int _e) : s(_s), e(_e), m((_s + _e) / 2), v(e - s + 1) {
if (s != e)
l = new node(s, m),
r = new node(m + 1, e);
}
void upd(int n) {
if (s == e) {
v = 1 - v;
return;
}
if (n <= m)
l->upd(n);
else
r->upd(n);
v = l->v + r->v;
}
int qry(int a, int b) {
if (s > b || e < a)
return 0;
if (a <= s && b >= e)
return v;
return l->qry(a, b) + r->qry(a, b);
}
} *root;
signed main() {
int n;
string s;
cin >> n >> s;
map<int, int> freq;
for (int i = 0; i < n; i++) {
freq[s[i]]++;
}
for (int i = n; i < 2 * n; i++) {
freq[s[i]]--;
}
for (int i = 'a'; i <= 'z'; i++)
freq[i] /= 2;
vector<bool> moved(n, false);
int ans = 0, count = 0;
for (int i = n - 1; i >= 0; i--) {
if (freq[s[i]] > 0) {
moved[i] = true;
count++;
ans += n - count - i;
freq[s[i]]--;
}
}
int orgcount = count;
string s1 = "";
for (int i = 0; i < n; i++) {
if (!moved[i])
s1 += s[i];
}
for (int i = 0; i < n; i++) {
if (moved[i])
s1 += s[i];
}
for (int i = n; i < 2 * n; i++) {
s1 += s[i];
}
moved = vector<bool>(n, false);
for (int i = n; i < 2 * n; i++) {
if (freq[s[i]] < 0) {
moved[i] = true;
ans += i - n + count;
count--;
freq[s[i]]++;
}
}
string crnt, ref;
for (int i = 0; i < n - orgcount; i++) {
crnt += s1[i];
}
for (int i = n; i < 2 * n; i++) {
if (moved[i])
crnt += s[i];
}
for (int i = n - orgcount; i < n; i++) {
ref += s1[i];
}
for (int i = n; i < 2 * n; i++) {
if (!moved[i])
ref += s[i];
}
vector<queue<int>> indices(26, queue<int>());
for (int i = 0; i < n; i++)
indices[ref[i] - 'a'].push(i);
root = new node(0, n - 1);
for (int i = 0; i < n; i++) {
int crntind = indices[crnt[i] - 'a'].front();
indices[crnt[i] - 'a'].pop();
root->upd(crntind);
ans += root->qry(0, crntind);
}
cout << ans << '\n';
}
