// Super Idol的笑容
// 都没你的甜
// 八月正午的阳光
// 都没你耀眼
// 热爱105°C的你
// 滴滴清纯的蒸馏水
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
#define ll long long
#define ii pair<ll,ll>
#define iii pair<ii,ll>
#define fi first
#define se second
#define endl '\n'
#define debug(x) cout << #x << ": " << x << endl
#define pub push_back
#define pob pop_back
#define puf push_front
#define pof pop_front
#define lb lower_bound
#define ub upper_bound
#define rep(x,start,end) for(auto x=(start)-((start)>(end));x!=(end)-((start)>(end));((start)<(end)?x++:x--))
#define all(x) (x).begin(),(x).end()
#define sz(x) (int)(x).size()
#define indexed_set tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>
//change less to less_equal for non distinct pbds, but erase will bug
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
int fen[100005];
void upd(int i,int j){
while (i<100005){
fen[i]+=j;
i+=i&-i;
}
}
int query(int i){
int res=0;
while (i){
res+=fen[i];
i-=i&-i;
}
return res;
}
int n;
string s;
vector<int> v[26];
bool pos[200005];
vector<int> p1[26];
vector<int> p2[26];
int arr[100005];
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin.exceptions(ios::badbit | ios::failbit);
cin>>n;
cin>>s;
rep(x,0,2*n){
v[s[x]-'a'].pub(x);
}
rep(x,0,26){
rep(y,0,sz(v[x])/2) pos[v[x][y]]=true;
}
ll ans=0;
ll curr=0;
//rep(x,0,2*n) cout<<pos[x]<<" "; cout<<endl;
rep(x,0,2*n){
if (!pos[x]) curr++;
else ans+=curr;
}
int i1=0,i2=0;
rep(x,0,2*n){
if (!pos[x]) p1[s[x]-'a'].pub(i1++);
else p2[s[x]-'a'].pub(i2++);
}
rep(x,0,26){
rep(y,0,sz(p1[x])) arr[p1[x][y]]=p2[x][y];
}
rep(x,2,n+1) upd(x,1);
rep(x,0,n){
ans+=query(arr[x]+1)-x;
upd(1,1);
upd(arr[x]+1,-1);
}
cout<<ans<<endl;
}
