#include <bits/stdc++.h>
using std::vector;
using std::array;
using std::pair;
using std::tuple;
struct Fenwick {
int size;
vector<int> data;
Fenwick(const int n) : size(n), data(n + 1) {}
void add(int i, const int x) {
i += 1;
while (i <= size) {
data[i] += x;
i += i & -i;
}
}
int pref(int i) const {
int ret = 0;
while (i > 0) {
ret += data[i];
i -= i & -i;
}
return ret;
}
int sum(const int l, const int r) const {
return pref(r) - pref(l);
}
};
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
int N;
std::cin >> N;
vector<char> S(2 * N);
array<vector<int>, 26> idx = {};
for (int i = 0; i < 2 * N; ++i) {
std::cin >> S[i];
idx[S[i] - 'a'].push_back(i);
}
array<int, 26> count = {};
array<int, 2> len = {};
vector<int> to(2 * N), perm(N);
long long ans = 0;
for (int i = 0; i < 2 * N; ++i) {
const int k = S[i] - 'a';
const int h = idx[k].size() / 2;
if (count[k] >= h) {
to[i] = N + len[1];
len[1] += 1;
perm[to[i] - N] = to[idx[k][count[k] - h]];
} else {
to[i] = len[0];
len[0] += 1;
ans += std::abs(to[i] - i);
}
count[k] += 1;
}
Fenwick fen(N);
for (const int x : perm) {
ans += fen.sum(x + 1, N);
fen.add(x, 1);
}
std::cout << ans << '\n';
return 0;
}
