#include <bits/stdc++.h>

using namespace std;

ifstream f("litere.in");
ofstream g("litere.out");

int sortare(int min, int max, char a[10001]){
    int count = 0;
    char aux;
    bool sortat = 1;
    do {
        sortat = 1;
        for (int i = min; i < max; i++){
            if (a[i] > a[i + 1]){
                aux = a[i];
                a[i] = a[i + 1];
                a[i + 1] = aux;
                count++;
                sortat = 0;
            }    
        }
    } while (sortat == 0);
    return count;
}

int main(void){
    char a[10001];
    int n = 0;
    f >> n; f.get();

    for (int i = 0; i < n; i++){
        f.get(a[i]);
    }

    g << sortare(0, n - 1, a);

    return 0;
}