#include <bits/stdc++.h>
//#define DEBUG 1106
#define int long long
#define ll long long
#define ld long double
#define pb emplace_back
#define p_q priority_queue
#define m_p make_pair
#define pii pair<int,int>
#define endl '\n'
#define INIT ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define FOR(i,a,b) for(int i = a; i <= b; i++)
#define forn(i,n) for (int i = 0; i < n; i++)
#define forn1(i,n) for (int i = 1; i <= n; i++)
#define all(x) x.begin(),x.end()
#define ft first
#define sd second
#define lowbit(x) (x&(-x))
#define chmax(x,y) x=max(x,y)
#define chmin(x,y) x=min(x,y)
#ifdef DEBUG
#define debug(x) cout << #x << ": " << x << endl;
#else
#define debug(x) 1106;
#endif
using namespace std;
const int N = 1e6+5;
const int M = 2005;
const int inf = 1e9;
const int INF = 1e18;
const int MOD = 1e9+7;
int a[N], b[N];
int cnt[27], c[27];
int s1[N], s2[N];
int BIT[N], n;
int num[N];
void update(int x, int y) {
for(; x <= n; x += lowbit(x)) {
BIT[x] += y;
}
}
int query(int x) {
int sum = 0;
for(; x; x -= lowbit(x))
sum += BIT[x];
return sum;
}
int tot = 0;
int r(int x) {
return lower_bound(num+1,num+1+tot,x)-num;
}
signed main() {
INIT
#ifdef DEBUG
freopen("input.txt", "r", stdin);
#endif
///////////
cin >> n;
char ch;
forn(i,2*n) {
cin >> ch;
int t = ch-'a';
a[i] = t;
b[i] = cnt[t];
cnt[t]++;
}
forn(i,26) cnt[i]/=2;
int x = 0, y = 0, ret = 0;
map<pii,int> mp;
forn(i,2*n) {
if(b[i] < cnt[a[i]]) {
ret += (i-x);
s1[x] = a[i];
mp[m_p(a[i],b[i])] = x;
x++;
} }
forn(i,2*n) {
if(b[i] >= cnt[a[i]]) {
s2[y] = mp[m_p(a[i],c[a[i]])];
c[a[i]]++;
y++;
}
}
tot = 0;
int ans = 0;
for(int i = 1; i <= n; i++) {
a[i] = s2[i-1];
num[i]=a[i];
}
sort(num+1,num+1+n);
for (int i = 1; i <= n; i++) {
if(i==1||num[i]!=num[i-1]) num[++tot]=num[i];
}
for (int i = 1; i <= n; i++) {
a[i] = r(a[i]);
}
for (int i = 1; i <= n; i++) {
ans += i-1-query(a[i]);
update(a[i],1);
}
cout << ans + ret;
}
