#include <fstream>
#include <cstring>

using namespace std;

int n;
char sir[10005];

int frecv[26];

int main()
{
    ifstream cin("litere.in");
    ofstream cout("litere.out");

    cin >> n; cin.get();
    cin.get(sir + 1, 10005);

    int ans = 0, j;
    for (int i = 1; i <= n; ++ i) {
        ans += frecv[25] - frecv[sir[i] - 'a'];
        for (j = sir[i] - 'a'; j < 26; ++ j)
            ++ frecv[j];
    }

    cout << ans << '\n';

    cin.close();
    cout.close();
    return 0;
}