#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
struct node {
int s, e;
ll mn, mx, sum;
bool lset;
ll add_val, set_val;
node *l, *r;
node (int _s, int _e, int A[] = NULL): s(_s), e(_e), mn(0), mx(0), sum(0), lset(0), add_val(0), set_val(0), l(NULL), r(NULL) {
if (A == NULL) return;
if (s == e) mn = mx = sum = A[s];
else {
l = new node(s, (s+e)>>1, A), r = new node((s+e+2)>>1, e, A);
combine();
}
}
void create_children() {
if (s == e) return;
if (l != NULL) return;
int m = (s+e)>>1;
l = new node(s, m);
r = new node(m+1, e);
}
void self_set(ll v) {
lset = 1;
mn = mx = set_val = v;
sum = v * (e-s+1);
add_val = 0;
}
void self_add(ll v) {
if (lset) { self_set(v + set_val); return; }
mn += v, mx += v, add_val += v;
sum += v*(e-s+1);
}
void lazy_propagate() {
if (s == e) return;
if (lset) {
l->self_set(set_val), r->self_set(set_val);
lset = set_val = 0;
}
if (add_val != 0) {
l->self_add(add_val), r->self_add(add_val);
add_val = 0;
}
}
void combine() {
if (l == NULL) return;
sum = l->sum + r->sum;
mn = min(l->mn, r->mn);
mx = max(l->mx, r->mx);
}
void add(int x, int y, ll v) {
if (s == x && e == y) { self_add(v); return; }
int m = (s+e)>>1;
create_children(); lazy_propagate();
if (x <= m) l->add(x, min(y, m), v);
if (y > m) r->add(max(x, m+1), y, v);
combine();
}
void set(int x, int y, ll v) {
if (s == x && e == y) { self_set(v); return; }
int m = (s+e)>>1;
create_children(); lazy_propagate();
if (x <= m) l->set(x, min(y, m), v);
if (y > m) r->set(max(x, m+1), y, v);
combine();
}
ll range_sum(int x, int y) {
if (s == x && e == y) return sum;
if (l == NULL || lset) return (sum / (e-s+1)) * (y-x+1);
int m = (s+e)>>1;
lazy_propagate();
if (y <= m) return l->range_sum(x, y);
if (x > m) return r->range_sum(x, y);
return l->range_sum(x, m) + r->range_sum(m+1, y);
}
ll range_min(int x, int y) {
if (s == x && e == y) return mn;
if (l == NULL || lset) return mn;
int m = (s+e)>>1;
lazy_propagate();
if (y <= m) return l->range_min(x, y);
if (x > m) return r->range_min(x, y);
return min(l->range_min(x, m), r->range_min(m+1, y));
}
ll range_max(int x, int y) {
if (s == x && e == y) return mx;
if (l == NULL || lset) return mx;
int m = (s+e)>>1;
lazy_propagate();
if (y <= m) return l->range_max(x, y);
if (x > m) return r->range_max(x, y);
return max(l->range_max(x, m), r->range_max(m+1, y));
}
~node() {
if (l != NULL) delete l;
if (r != NULL) delete r;
}
} *root;
int main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
ll n;
cin >> n;
string s;
cin >> s;
ll alph[30],a2[30];
memset(alph,0,sizeof(alph));
memset(a2,0,sizeof(a2));
for (int i=0;i<s.size();i++){
alph[s[i]-'a']++;
}
ll ord[n*2+5];
ll count=0;
vector<int> target,curr;
ll total=0;
queue<ll> diff[30];
for (int i=0;i<s.size();i++){
if (a2[s[i]-'a']>=alph[s[i]-'a']/2) {
ord[i] = 2;
curr.push_back(s[i]-'a');
count++;
diff[s[i]-'a'].push(count-1);
}
else {
ord[i] = 1;
target.push_back(s[i]-'a');
total += count;
}
a2[s[i]-'a']++;
}
root = new node(0,n+5);
root->set(0,n+5,1);
for (int i=0;i<n;i++){
ll ind = diff[target[i]].front();
if (ind-1>=0) total += root->range_sum(0,ind-1);
root->set(ind,ind,0);
diff[target[i]].pop();
}
cout << total;
}
