#include <bits/stdc++.h>
using namespace std;
#define fast ios::sync_with_stdio(0);cin.tie(0);
#define s second
#define f first
typedef long long ll;
const ll MOD = 1e9 + 7;
const ll LOGN = 20;
const ll MAXN = 2e5 + 5;
vector<int> occ[26];
vector<int> leftV, rightV;
ll fen[MAXN];
void update(int k) {
while (k < MAXN) {
fen[k]++;
k += k&-k;
}
}
ll query(int k) {
ll res = 0;
while (k >= 1) {
res += fen[k];
k -= k&-k;
}
return res;
}
int main() {
fast
int n;
string s;
cin >> n >> s;
s = "#" + s;
for (int i = 1; i <= 2*n; i++)
occ[s[i]-'a'].push_back(i);
for (int i = 0; i < 26; i++) {
int q = occ[i].size() / 2;
for (int j = 0; j < q; j++)
leftV.push_back(occ[i][j]);
for (int j = q; j < 2*q; j++)
rightV.push_back(occ[i][j]);
}
sort(leftV.begin(), leftV.end());
sort(rightV.begin(), rightV.end());
vector<int> occ2[26];
for (int i = n-1; i >= 0; i--) {
occ2[s[leftV[i]] - 'a'].push_back(i+1);
}
vector<int> inv;
for (auto u : rightV) {
int ch = s[u] - 'a';
inv.push_back(occ2[ch].back());
occ2[ch].pop_back();
}
ll ans = 0;
for (int i = 0; i < n; i++) {
ans += i - query(inv[i]);
update(inv[i]);
}
memset(fen, 0, sizeof(fen));
for (auto u : rightV)
leftV.push_back(u);
for (int i = 0; i < 2*n; i++) {
ans += i - query(leftV[i]);
update(leftV[i]);
}
cout << ans << "\n";
}
