#include <bits/stdc++.h>
using namespace std;
const int N = 1e6+2;
const int mod = 1e9 + 7;
string s;
int n, fr[2][26], total[26], plm[200002];
struct AIB {
int n;
vector<int>aib;
AIB(int N): n(N), aib(N+2) {}
void update (int x, int val) {
for (int i = x; i <= n; i += (i & -i))
aib[i] += val;
}
int query (int x) {
int s = 0;
for (int i = x; i; i -= (i & -i))
s += aib[i];
return s;
}
};
using ll = long long;
ll CountSteps(string s1, string s2, int size)
{
AIB pom(size);
deque<int>poz[26];
for (int i = 0; i < size; i++)
poz[s1[i] - 'a'].push_back(i);
ll ans = 0;
for (int i = 0; i < size; i++) {
int k = poz[s2[i] - 'a'].front();
poz[s2[i] - 'a'].pop_front();
ans += pom.query(size - k);
pom.update(size - k, 1);
}
return ans;
}
int main ()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
cin >> n;
cin >> s;
for (int i = 0; i < 2 * n; i++) {
fr[i / n][s[i] - 'a']++;
}
for (int i = 0; i < 26; i++)
total[i] = fr[0][i] + fr[1][i];
deque<char>q1, q2;
int stop = n;
int ans = 0;
for (int i = n - 1; i >= 0; i--) {
if (fr[0][s[i] - 'a'] > total[s[i] - 'a'] / 2) {
ans += stop - i;
stop--;
q1.push_front(s[i]);
plm[i] = '?';
fr[0][s[i] - 'a']--;
}
}
stop = n-1;
for (int i = n; i < 2 * n; i++) {
if (fr[1][s[i] - 'a'] > total[s[i] - 'a'] / 2) {
q2.push_back(s[i]);
ans += i - stop;
stop++;
plm[i] = '?';
fr[1][s[i] - 'a']--;
}
}
string a, b;
for (int i = 0; i < n; i++)
if (plm[i] != '?')
a += s[i];
for (auto it : q2) a += it;
for (auto it : q1) b += it;
for (int i = n; i < 2 * n; i++)
if (plm[i] != '?')
b += s[i];
//cout << a << " " << b << "\n";
cout << CountSteps(a, b, n) + CountSteps(s, a + b, 2 * n);
return 0;
}
