#include <fstream>
#include <cstring>

using namespace std;

ifstream in("litere.in");
ofstream out("litere.out");

const int MAX_LEN = 10000;
const int SIGMA = 26;

char S[MAX_LEN + 5];
int F[SIGMA];

int main() {
    int n, i, j, ans = 0;

    in >> n;
    in >> S + 1;

    for(i = n; i; i--) {
        F[S[i] - 'a']++;
        for(j = S[i] - 'a' - 1; j >= 0; j--) {
            ans += F[j];
        }
    }

    out << ans << '\n';
    return 0;
}