#include <bits/stdc++.h>
using namespace std;
int pos[26]; // pos[0]~pos[25] 分别存 'a'~'z' 最新出现的位置
int main()
{
    int n;
    string s;
    cin >> n;
    cin >> s;
    long long sum = 0;
    for (int i = 0; i < s.size(); i++)
    {
        sum += pos[s[i] - 'a'];
        pos[s[i] - 'a'] = i + 1;
    }
    cout << sum;
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    string s;
    cin >> n;
    cin >> s;
    long long sum = 0;
    for (int i = 0; i < s.size(); i++)
    {
        int pos = 0;
        for (int j = i - 1; j >= 0; j--)
            if (s[j] == s[i])
            {
                pos = j + 1;
                break;
            }
        sum += pos;
    }
    cout << sum;
    return 0;
}