#include <iostream>
#include <algorithm>
#include <utility>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
using namespace std;
int invcount(int *arr, int n){
if (n < 2) return 0;
int arr1[n / 2];
for (int i = 0; i < n / 2; i++) arr1[i] = arr[i];
int arr2[n - n / 2];
for (int i = n / 2; i < n; i++) arr2[i - n / 2] = arr[i];
int ans = invcount(arr1, n / 2) + invcount(arr2, n - n / 2);
int p1 = 0, p2 = 0;
while (p1 + p2 < n){
if (p2 == n - n / 2){
arr[p1 + p2] = arr1[p1];
p1++;
} else if (p1 == n / 2){
arr[p1 + p2] = arr2[p2];
p2++;
} else if (arr1[p1] < arr2[p2]){
arr[p1 + p2] = arr1[p1];
p1++;
} else {
arr[p1 + p2] = arr2[p2];
ans += n / 2 - p1;
p2++;
}
}
return ans;
}
int otherend[200000], rightend[100000];
pair<int, int> pairarr[100000];
int main(){
cin.tie(0);
ios_base::sync_with_stdio(0);
int n, cntr = 0, ans, closedcount = 0;
char c;
cin >> n;
vector<vector<int>> appr;
appr.resize(26);
for (int i = 0; i < 2 * n; i++){
cin >> c;
appr[c - 'a'].push_back(i);
}
for (int i = 0; i < 26; i++){
for (uint32_t j = 0; j < appr[i].size() / 2; j++){
otherend[appr[i][j]] = appr[i][j + appr[i].size() / 2];
otherend[appr[i][j + appr[i].size() / 2]] = appr[i][j];
pairarr[cntr] = {appr[i][j], appr[i][j + appr[i].size() / 2]};
cntr++;
}
}
sort(pairarr, pairarr + n);
for (int i = 0; i < n; i++) rightend[i] = pairarr[i].second;
ans = invcount(rightend, n);
for (int i = 0; i < 2 * n; i++){
if (i < otherend[i]) ans += closedcount;
else closedcount++;
}
cout << ans;
}
