#include <bits/stdc++.h>
using namespace std;
#define int long long
struct node{
int S, E, M, val=1;
node *left, *right;
node(int s, int e): S(s), E(e){
if(S==E){
val=1;
return;
}
M=S+(E-S)/2;
left=new node(S,M);
right=new node(M+1,E);
val=left->val+right->val;
}
void upd(int m, int x){
if(S==E){
val=x;
return;
}
if(m<=M){
left->upd(m,x);
}
else{
right->upd(m,x);
}
val=left->val+right->val;
}
int qry(int l, int r){
if(S>r||E<l){
return 0;
}
if(l<=S&&E<=r){
return val;
}
return left->qry(l,r)+right->qry(l,r);
}
}*segtree;
signed main(){
int n, ans=0;
cin >> n;
string s;
cin >> s;
segtree = new node(0,n-1);
//cout << s << " " << s[0]-'a' << endl;
vector<int> a(26,0), c(26,0);
for(int i=0; i<n; i++){
a[s[i]-'a']++;
a[s[n+i]-'a']++;
c[s[i]-'a']++;
}
string ms1="", ms2="", fs1="", fs2="";
int p=0;
for(int i=n-1; i>=0; i--){
if(c[s[i]-'a']>a[s[i]-'a']/2){
c[s[i]-'a']--;
ans+=n-i-1-p;
p++;
ms1+=s[i];
}
else{
fs1+=s[i];
}
}
p=0;
for(int i=n; i<n*2; i++){
if(c[s[i]-'a']<a[s[i]-'a']/2){
c[s[i]-'a']++;
ans+=i-n-p;
p++;
ms2+=s[i];
}
else{
fs2+=s[i];
}
}
ans+=p*p;
//cout << fs1 << " " << fs2 << " " << ms1 << " " << ms2 << endl;
stack<char> t;
for(int i=0; i<(long long)fs1.length(); i++){
t.push(fs1[i]);
}
for(int i=0; i<(long long)fs1.length(); i++){
fs1[i]=t.top();
t.pop();
}
for(int i=0; i<(long long)ms1.length(); i++){
t.push(ms1[i]);
}
for(int i=0; i<(long long)ms1.length(); i++){
ms1[i]=t.top();
t.pop();
}
fs1=fs1+ms2;
fs2=ms1+fs2;
//3cout << fs1 << " " << fs2 << endl;
vector<vector<int> >fn(26);
vector<int> in(26,0);
for(int i=0; i<(long long)fs2.length(); i++){
fn[fs2[i]-'a'].push_back(i);
}
for(int i=0; i<(long long)fs1.length(); i++){
//cout << fn[fs1[i]-'a'][in[fs1[i]-'a']] << endl;
//cout << segtree->qry(0,0) << endl;
ans+=segtree->qry(0,fn[fs1[i]-'a'][in[fs1[i]-'a']]-1);
//cout << ans << endl;
segtree->upd(fn[fs1[i]-'a'][in[fs1[i]-'a']],0);
in[fs1[i]-'a']++;
}
cout << ans << endl;
}
