#include <bits/stdc++.h>
using namespace std;

const string FILE_NAME = "litere";
ifstream fin(FILE_NAME + ".in");
ofstream fout(FILE_NAME + ".out");

int main() {
    int n, c = 0, st = 1;
    string s;

    fin >> n >> s;
    bool sortat = true;
    do{
        sortat = true;

        for(int i = st; i < n; i++){
            if(s[i] < s[i - 1]){
                if(sortat == true)
                    st--;
                swap(s[i], s[i - 1]);
                sortat = false;
                c++;
            }
            else if(sortat == true){
                st = i;
            }
        }

    }while(sortat != true);

    fout << c;

    return 0;
}