#include <fstream>
using namespace std;
char c;
int fv[27], i, n, j;
long long rez;
ifstream cin("litere.in");
ofstream cout("litere.out");
int main()
{   cin >> n;
    for(i = 1; i <= n; ++i){
        cin >> c;
        fv[c - 'a' + 1]++;
        for(j = c - 'a' + 2; j <= 26; ++j) rez += fv[j];
                          }
    cout << rez << '\n';
    return 0;
}