#include<fstream>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
int hz[200],x,n;
char v[10001];
long long sol;
int main (void) {
    in >> n;
    in >> v + 1;
    for (int i = 1; i <= n; i ++) {
        x = v[i] - 'a' + 1;
        hz[x] ++;
        for (int j = v[i] + 1; j <= 'z'; j ++) {
            sol += hz[j-'a'+1];
        }
    }
    out << sol;
    return 0;
}