#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
// Ofast, O0, O1, O2, O3, unroll-loops, fast-math, trapv
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
#define Mp make_pair
#define sep ' '
#define endl '\n'
#define F first
#define S second
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define kill(res) cout << res << '\n', exit(0);
#define set_dec(x) cout << fixed << setprecision(x);
#define fast_io ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io freopen("input.txt", "r", stdin) ; freopen("output.txt", "w", stdout);
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const ll A = 28;
const ll N = 2e5 + 50;
const ll Mod = 1e9 + 7;
ll n, num[N], ps[N];
string s, t1, t2;
vector<int> idx[A];
int bit[N];
void upd(int x, int y){
for(; x <= n; x += x & (-x)) bit[x] += y;
}
int get(int x){
ll out = 0;
for(; x; x &= x-1) out += bit[x];
return out;
}
int main(){
fast_io;
cin >> n >> s;
s = "$" + s;
for(int i = 0; i < A; i++){
int cnt = 0, c = 0;
for(int j = 1; j <= 2*n; j++) if(s[j] - 'a' == i) cnt++;
for(int j = 1; j <= 2*n; j++) if(s[j] - 'a' == i) num[j] = ((++c) <= cnt/2 ? 1 : 2);
}
ll sum = 0;
for(int i = 1; i <= 2*n; i++) ps[i] = ps[i-1] + num[i] - 1;
for(int i = 1; i <= 2*n; i++) sum += ps[i] * (num[i] == 1);
t1 = t2 = "$";
for(int i = 1; i <= 2*n; i++){
if(num[i] == 1) t1 += s[i];
else t2 += s[i];
}
for(int i = 0; i < A; i++){
for(int j = n; j > 0; j--) if(t2[j] - 'a' == i) idx[i].pb(j);
}
for(int i = 1; i <= n; i++){
upd(idx[t1[i] - 'a'].back(), 1); sum += idx[t1[i] - 'a'].back() - get(idx[t1[i] - 'a'].back());
idx[t1[i] - 'a'].pop_back();
}
cout << sum;
}
