// Problem: Writing Numbers
// Contest: CSES - CSES Problem Set
// URL: https://cses.fi/problemset/task/1086
// Memory Limit: 512 MB
// Time Limit: 1000 ms
//
// Powered by CP Editor (https://cpeditor.org)
#include <bits/stdc++.h>
using namespace std;
#define lg long long
const lg N = 2e5+5;
vector<lg> a[27];
lg loc[N], bit[N], m;
lg get(lg idx)
{
lg ans = 0;
while(idx)
{
ans += bit[idx];
idx -= (idx&(-idx));
}
return ans;
}
void upd(lg idx)
{
while(idx <= m)
{
bit[idx]++;
idx += (idx&(-idx));
}
}
int main()
{
lg n;
string s;
cin >> n >> s;
m = 2*n;
for(int i = 0; i < n*2; i++)
{
a[s[i]-'a'].push_back(i);
}
for(int i = 0; i < 26; i++)
{
lg x = a[i].size()/2;
for(int j = 0; j < x; j++)
{
loc[a[i][j]] = -1;
loc[a[i][j+x]] = 1;
}
a[i].clear();
}
string c = "", d = "";
lg ans = 0;
for(int i = 0; i < n*2; i++)
{
if(loc[i] == -1) c += s[i], ans += d.size(), loc[i] = c.size()-1;
else d += s[i], loc[i] = d.size()+n-1;
}
s = c+d;
for(int i = 0; i < n*2; i++)
{
a[s[i]-'a'].push_back(i);
}
for(int i = 0; i < 26; i++)
{
lg x = a[i].size()/2;
for(int j = 0; j < x; j++)
{
loc[a[i][j]] = a[i][j];
loc[a[i][j+x]] = loc[a[i][j]]+n;
}
}
for(int i = 2*n-1; i+1; i--)
{
ans += get(loc[i]+1);
upd(loc[i]+1);
}
cout << ans << '\n';
}
