#include <fstream>
#include <cstring>

using namespace std;

ifstream cin("litere.in");
ofstream cout("litere.out");

int main() {
    
    int n, cnt = 0;
    char s[10002];
    cin >> n;
    cin >> s;
    bool sortat = false;
    while(!sortat){
        sortat = true;
        for(int i = 0; i < n - 1; ++i){
            if(s[i] > s[i+1]){
                cnt++;
                sortat = false;
                swap(s[i], s[i+1]);
            }
        }
    }
    cout << cnt;
    return 0;
}