#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define fr first
#define sc second
#define pb push_back
#define endl "\n"
#define all(x) x.begin(),x.end()
#define sp << " " <<
#define inf 1e10
#define N 100000
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef tuple<int,int,int> tiii;
typedef pair<int,int> pii;
int ft[N+5];
void update(int n,int x,int val){
for(int i=x;i<=n;i+=(i&-i))
ft[i]+=val;
}
int get(int n,int x){
int ans=0;
for(int i=x;i>0;i-=(i&-i))
ans+=ft[i];
return ans;
}
int solve(int n,string s){
memset(ft,0,sizeof(ft));
int j=n,c=0;
vector<int> a(26,0);
for(int i=0;i<2*n;i++){
if(i<j) a[s[i]-'a']++;
else a[s[i]-'a']--;
}
for(int i=0;i<26;i++)
if(a[i]<0) c++;
for(;j<2*n;j++){
if(!c) break;
a[s[j]-'a']+=2;
if(a[s[j]-'a']==0)
c--;
}
j--;
int ans=0;
vector<char> str1,str2;
for(int i=j;i>=0;i--){
if(a[s[i]-'a']>0){
a[s[i]-'a']-=2;
str2.pb(s[i]);
ans+=j-i;
j--;
}
else
str1.pb(s[i]);
}
reverse(all(str1));
reverse(all(str2));
for(int i=n+str2.size();i<2*n;i++)
str2.pb(s[i]);
//~ cout << ans << endl;
//~ for(auto i:str1) cout << i;cout << endl;
//~ for(auto i:str2) cout << i;cout << endl;
queue<int> q[26];
vector<int> v;
for(int i=0;i<n;i++)
q[str1[i]-'a'].push(i);
for(int i=0;i<n;i++){
int t=q[str2[i]-'a'].front();
q[str2[i]-'a'].pop();
ans+=t-i+get(n,n-t);
update(n,n-t,1);
}
return ans;
}
int32_t main(){
//~ freopen("a.txt","r",stdin);
//~ freopen("a.txt","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);cout.tie(NULL);
int n;
string s;
cin >> n >> s;
int ans=solve(n,s);
cout << ans << endl;
}
