#include <bits/stdc++.h>
using namespace std;
#define int long long
vector<int> tree;
void update(int pos, int i, int f, int idx){
if(i == f and i == idx){
tree[pos]++;
return;
}
int meio = (i+f)/2;
if(idx <= meio) update(2*pos+1, i, meio, idx);
else update(2*pos+2, meio+1, f, idx);
tree[pos] = tree[2*pos+1] + tree[2*pos+2];
return;
}
int query(int pos, int i, int f, int l, int r){
if(l<=i and f<=r){
return tree[pos];
}
int meio =(i+f)/2;
int res = 0;
if(l <= meio) res += query(2*pos+1, i, meio, l, r);
if(r > meio) res += query(2*pos+2, meio+1, f, l, r);
return res;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
vector<vector<int>> letra(30);
int n; cin >> n;
n *=2;
tree.assign(4*(n+1), 0);
string s; cin >> s;
for(int i=0; i<n; i++){
int nmr = s[i] - 'a';
letra[nmr].push_back(i);
}
string inicio = "", fim = "";
vector<int> qnt(30,0);
int esq = 0, dir = 0;
int res = 0;
for(int i=0; i<n; i++){
int nmr = s[i] - 'a';
if(i<n/2){
if(qnt[nmr]< (letra[nmr].size()/2)){
inicio+=s[i];
}
else{
fim += s[i];
dir++;
}
}
else{
if(qnt[nmr]< (letra[nmr].size()/2)){
inicio+=s[i];
esq++;
}
else{
fim += s[i];
}
}
qnt[nmr]++;
}
res += dir*esq;
int ii= 0, ff = 0;
qnt.assign(30,0);
for(int i=0; i<n; i++){
int nmr = s[i] - 'a';
if(i<n/2){
if(qnt[nmr]>= (letra[nmr].size()/2)){
res += (n/2-1 - (dir-ii) + 1 - i);
ii++;
}
}
else{
if(qnt[nmr]< (letra[nmr].size()/2)){
res += (i - (n/2 + ff));
ff++;
}
}
qnt[nmr]++;
}
s = inicio + fim;
for(int i=0; i<30; i++) letra[i].clear();
for(int i=0; i<n; i++){
int nmr = s[i] - 'a';
letra[nmr].push_back(i);
}
qnt.assign(30,0);
for(int i = 0; i<n/2; i++){
int nmr = s[i] - 'a';
int sz = letra[nmr].size();
sz/=2;
int posicao = letra[nmr][sz + qnt[nmr]];
res += query(0,0,n,posicao, n);
update(0,0,n, posicao);
qnt[nmr]++;
}
cout << res << endl;
}
