#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int MAXN = 2e5+5;
#define all(x) x.begin(), x.end()
#define sz(x) (int)x.size()
#define pb push_back
#define fr first
#define sc second
int n, bit[MAXN];
string v;
vector<int> L[26];
void update(int x, int val) {
for( ; x <= n; x += x&-x)
bit[x] += val;
}
int sum(int x) {
int cnt = 0;
while(x > 0) {
cnt += bit[x];
x -= x&-x;
}
return cnt;
}
int main() {
cin >> n >> v;
n *= 2;
for(int i = 0; i < n; i++) L[v[i] - 'a'].pb(i+1);
vector<pii> p;
for(int i = 0; i < 26; i++)
for(int j = 0; j < sz(L[i])/2; j++)
p.pb({L[i][j], L[i][j + sz(L[i])/2]});
vector<int> flag(n+1);
for(auto [a,b] : p) flag[a] = -1, flag[b] = a;//, cout << a << " " << b << "\n";
ll ans = 0;
for(int i = 1; i <= n; i++) {
if(flag[i] != -1) {
update(flag[i], -1);
ans += sum(flag[i]);
}
else {
update(i, 1);
int x = sum(i-1);
ans += ((i-1) - x)/2;
}
}
cout << ans << "\n";
}
