#include<bits/stdc++.h>
using namespace std;
map<char,int>freq;
const int maxn = 200001;
vector<int>exclnt;
deque<int>dex[200];
vector<int>ord;
int segtree[6*maxn]={0};
void update(int idx, int low, int high, int val) {
if(low==val && high==val) {
segtree[idx]=1;
return;
}
if(val<low || val>high) {
return;
}
int mid = (low+high)/2;
update(2*idx,low,mid,val);
update(2*idx+1, mid+1,high,val);
segtree[idx] = segtree[2*idx] + segtree[2*idx+1];
}
int quer(int idx, int low, int high, int l, int r) {
if(low>=l && high<=r) {
return segtree[idx];
}
if(low>r || high<l) return 0;
int mid = (low+high)/2;
return quer(2*idx,low,mid,l,r)+quer(2*idx+1,mid+1,high,l,r);
}
int main() {
int n;
string gab;
cin >> n;
cin >> gab;
n = n*2;
for(int i=0; i<gab.size(); i++) freq[gab[i]]++;
for(int i=0; i<n; i++) {
if(freq[gab[i]] > 0) {
exclnt.push_back(gab[i]);
freq[gab[i]]-=2;
}
}
int ukex = exclnt.size();
for(int i=0; i<ukex; i++) {
exclnt.push_back(exclnt[i]);
}
for(int i=0; i<n; i++) {
dex[exclnt[i]].push_back(i);
}
for(int i=0; i<n; i++) {
ord.push_back(dex[gab[i]].front());
dex[gab[i]].pop_front();
}
int ans=0;
for(int i=0; i<n; i++) {
ans+=quer(1,1,n-1,ord[i],n-1);
update(1,1,n-1,ord[i]);
}
cout << ans << endl;
return 0;
}
