#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
char s[10001];
int main()
{
    ifstream in("litere.in");
    ofstream out("litere.out");
    int lmax = 0, k = 0, n;
    in >> n;
    in.getline(s, n + 1);
    in.getline(s, n + 1);
    for (int i = 1;i < n;i++){
        for (int j = 0;j < i;j++) {
            if (s[j] > s[i]) {
                k++;
            }
        }
    }
    out << k;
    return 0;
}
//cout << cuv[poz];