#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
typedef long long ll;
typedef long double ld;
using namespace std;
using namespace __gnu_pbds;
using ordered_set = tree<ll, null_type, less<ll>, rb_tree_tag, tree_order_statistics_node_update>;
#define all(x) x.begin(), x.end()
#define pll pair<ll, ll>
#define fast ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)
const ll mod = 998244353;
ld fpow(ll a, ll b, ll m = -1)
{
if (m != -1)
a %= m;
ll res = 1;
while (b > 0)
{
if (b % 2 == 1)
{
if (m != -1)
res = res * a % m;
else
{
res *= a;
}
}
a = a * a;
if (m != -1)
{
a %= m;
}
b /= 2;
}
return res;
}
int main()
{
fast;
// freopen("pails.in", "r", stdin);
// freopen("pails.out", "w", stdout);
ll t = 1;
// cin >> t;
while (t--)
{
ll n;
cin >> n;
string s;
cin >> s;
vector<ll> freq(200);
for (int i = 0; i < 2 * n; i++)
{
freq[s[i]]++;
}
string s2, t;
vector<ll> freq2(200);
ll ans = 0;
for (int i = 0; i < 2 * n; i++)
{
freq2[s[i]]++;
if (freq2[s[i]] > freq[s[i]] / 2)
{
t.push_back(s[i]);
}
else
{
s2.push_back(s[i]);
ans+=t.size();
}
}
// cout << t << ' ';
vector<set<ll>> v(200);
for (int i = 0; i < n; i++)
{
v[t[i]].insert(i);
}
ordered_set os;
for (int i = 0; i < n; i++)
{
// if (v[s[i]].empty())
// continue;
os.insert(*v[s2[i]].begin());
ans += (*v[s2[i]].begin()) - os.order_of_key(*v[s2[i]].begin());
// cout << ans << ' ';
v[s2[i]].erase(v[s2[i]].begin());
}
cout << ans << '\n';
}
return 0;
}
