#include <bits/stdc++.h>
using namespace std;
#define m_p make_pair
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define fi first
#define se second
typedef long long ll;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
mt19937 rnf(2106);
const int N = 200005;
int n;
char a[N];
int m;
char b[N];
int u[N];
int t[N];
void ubd(int x, int y)
{
while (x <= n * 2)
{
t[x] += y;
x += (x & (-x));
}
}
int qry(int x)
{
int ans = 0;
while (x)
{
ans += t[x];
x -= (x & (-x));
}
return ans;
}
void solv()
{
cin >> n;
cin >> (a + 1);
int q[26] = {};
for (int i = 1; i <= n * 2; ++i)
{
q[a[i] - 'a']++;
}
for (int i = 0; i < 26; ++i)
q[i] /= 2;
for (int i = 1; i <= n * 2; ++i)
{
if (q[a[i] - 'a'])
{
b[++m] = a[i];
--q[a[i] - 'a'];
}
}
for (int i = n + 1; i <= n * 2; ++i)
{
b[i] = b[i - n];
}
vector<int> v[26];
for (int i = 1; i <= n * 2; ++i)
{
v[b[i] - 'a'].push_back(i);
}
for (int i = n * 2; i >= 1; --i)
{
u[i] = v[a[i] - 'a'].back();
v[a[i] - 'a'].pop_back();
}
ll ans = 0;
for (int i = n * 2; i >= 1; --i)
{
ans += qry(u[i]);
ubd(u[i], 1);
}
cout << ans << "\n";
}
int main()
{
#ifdef SOMETHING
freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
#endif // SOMETHING
ios_base::sync_with_stdio(false), cin.tie(0);
int tt = 1;
//cin >> tt;
while (tt--)
{
solv();
}
return 0;
}
