//source:
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 2e5 + 10, M = 26;
int a[N], cnt[M];
queue<int> pos[M];
struct BinaryIndexedTree {
int bit[N];
void up(int x, int val) {
while (x) {
bit[x] += val;
x -= x & (-x);
}
}
int get(int x) {
int ret = 0;
while (x < N) {
ret += bit[x];
x += x & (-x);
}
return ret;
}
} bit;
signed main() {
cin.tie(0)->sync_with_stdio(0);
#ifdef LOCAL_MACHINE
if (fopen("task.inp", "r")) {
freopen("task.inp", "r", stdin);
freopen("task.out", "w", stdout);
}
#endif
int n; cin >> n;
string s; cin >> s;
for (int i = 0; i < 2 * n; ++i) ++cnt[a[i] = s[i] - 'a'];
for (int i = 0; i < M; ++i) cnt[i] /= 2;
vector<int> b;
for (int i = 0; i < 2 * n; ++i) if (cnt[a[i]]) {
b.push_back(a[i]);
--cnt[a[i]];
}
for (int i = 0; i < n; ++i) b.push_back(b[i]);
for (int i = 0; i < 2 * n; ++i) pos[b[i]].push(i + 1);
ll res = 0;
for (int i = 0; i < 2 * n; ++i) {
int x = pos[a[i]].front(); pos[a[i]].pop();
res += bit.get(x); bit.up(x, 1);
}
cout << res << "\n";
}
// ඞඞඞඞඞ you sus
