#include <fstream>
#include <cstring>

using namespace std;

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

int main() 
{
    int n, count = 0;
    fin >> n;
    fin.ignore();

    char s[10001];
    fin >> s;

    int len = strlen(s);
    for (int i = 0; i < len - 1; i++)
        for (int j = i + 1; j < len; j++)
            if (s[i] > s[j])
                count ++;

    fout << count;

    return 0;
}