#include <fstream>
#include <cstring>
using namespace std;
ifstream cin("litere.in");
ofstream cout("litere.out");
const int dim = 10001;
char s[dim];

int main()
{
    int n, cnt = 0;
    cin >> n >> s;
    bool sortat = false;

    while (!sortat) {
        sortat = true;

        for (int i = 0; i < n - 1; ++i)
        {
            if (s[i] > s[i + 1])
            {
                swap(s[i], s[i + 1]);
                cnt ++;
                sortat = false;
            }
        }
    }
    cout << cnt;
}