#include <iostream>
#include <cstring>
#include <fstream>

using namespace std;

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

int main()
{
    unsigned int n, i, j, contor = 0;
    bool ok;
    fin>>n;
    char litere[10002];
    fin.get();
    fin.get(litere, n + 1);
    for(i = 0; i < n - 1; i++){
        ok = false;
        for(j = 0; j < n - i - 1; j++){
            if(litere[j] > litere[j + 1]){
                swap(litere[j], litere[j + 1]);
                contor++;
                ok = true;
                }
            }
        if(!ok)
            break;
        }
    fout<<contor;
}