#include <fstream>
#define DIM 10001

using namespace std;

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

int bubbleSort(int len, char str[]) {
    int swaps = 0;
    bool sorted;

    do {
        sorted = true;
        for (int i = 0; i < len - 1; i++) {
            if (str[i] > str[i + 1]) {
                swap(str[i], str[i + 1]);
                swaps++;
                sorted = false;
            }
        }
    } while (!sorted);

    return swaps;
}

int main() {
    int n;
    char s[DIM];

    fin >> n >> s;
    fout << bubbleSort(n, s);

    return 0;
}