#include "bits/stdc++.h"
using namespace std;
#define int long long
#define INF 1000000000000000000
#define MOD 1000000007
int fw[100005];
void update(int x, int v) {
for(x++; x < 100005; x += x&-x) fw[x] += v;
}
int query(int x) {
int ans = 0;
for(x++; x; x -= x&-x) ans += fw[x];
return ans;
}
int query(int x, int y) {
return query(y)-query(x-1);
}
int32_t main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int n, ans = 0;
string s;
cin >> n >> s;
vector<int> occ[26];
for(int i = 0; i < 2*n; i++) occ[s[i]-'a'].push_back(i);
int pos[2*n], mp[2*n], cnt = 0;
memset(pos, 0, sizeof(pos));
for(int i = 0; i < 26; i++) {
for(int j = 0; j < occ[i].size()/2; j++) {
pos[occ[i][j]] = 1;
mp[occ[i][j]] = occ[i][j+occ[i].size()/2];
}
}
for(int i = 0; i < 2*n; i++) {
if(pos[i] == 0) cnt++;
else ans += cnt;
}
cnt = 2;
for(int i = 0; i < 2*n; i++) {
if(pos[i] == 1) pos[mp[i]] = cnt++;
}
for(int i = 0; i < 2*n; i++) if(pos[i] > 1) {
ans += query(pos[i], n+3);
update(pos[i], 1);
}
cout << ans << '\n';
}
