#include <bits/stdc++.h>
//#include "includeall.h"
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
#define endl '\n'
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define input(x) scanf("%lld", &x);
#define input2(x, y) scanf("%lld%lld", &x, &y);
#define input3(x, y, z) scanf("%lld%lld%lld", &x, &y, &z);
#define input4(x, y, z, a) scanf("%lld%lld%lld%lld", &x, &y, &z, &a);
#define print(x, y) printf("%lld%c", x, y);
#define show(x) cerr << #x << " is " << x << endl;
#define show2(x,y) cerr << #x << " is " << x << " " << #y << " is " << y << endl;
#define show3(x,y,z) cerr << #x << " is " << x << " " << #y << " is " << y << " " << #z << " is " << z << endl;
#define all(x) x.begin(), x.end()
#define discretize(x) sort(x.begin(), x.end()); x.erase(unique(x.begin(), x.end()), x.end());
#define FOR(i, x, n) for (ll i =x; i<=n; ++i)
#define RFOR(i, x, n) for (ll i =x; i>=n; --i)
#pragma GCC optimize("O3","unroll-loops")
using namespace std;
mt19937_64 rnd(chrono::steady_clock::now().time_since_epoch().count());
//using namespace __gnu_pbds;
//#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
//#define ordered_multiset tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>
typedef long long ll;
typedef long double ld;
typedef pair<ld, ll> pd;
typedef pair<string, ll> psl;
typedef pair<ll, ll> pi;
typedef pair<pi, ll> pii;
typedef pair<pi, pi> piii;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll n;
string ss, neww;
ll freq[30], cnt[30];
deque<ll> idx[30];
vector<ll> fenwick(250005,0);
ll ps(ll i)
{
if (i==0) return 0;
ll sum=0;
while (i>0)
{
sum+=fenwick[i];
i-=i&(-i);
}
return sum;
}
void update(ll i, ll v)
{
while (i<fenwick.size())
{
fenwick[i]+=v;
i+=i&(-i);
}
}
int main()
{
cin >> n >> ss;
//show(ss);
for (ll i=0; i<2*n; ++i) {freq[ss[i]-'a']++; idx[ss[i]-'a'].pb(i + 1);}
for (ll i=0; i<2*n; ++i) if ((++cnt[ss[i]-'a']) <= freq[ss[i]-'a']/2) {neww += ss[i];}
//show(neww);
neww += neww; neww = '.' + neww;
assert(neww.length() == 2*n + 1);
for (ll i=1; i<=2*n; ++i) update(i, 1);
ll ans = 0;
for (ll i=1; i<=2*n; ++i)
{
ll cur = idx[neww[i]-'a'].front();
ans += ps(cur-1);
update(cur, -1);
idx[neww[i]-'a'].pop_front();
}
cout << ans << endl;
return 0;
}
