#include <fstream>
#define DIM 10005
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,i,cnt;
char s[DIM];
bool ok;
int main() {
    fin>>n>>s;
    ok=0;
    while (ok==0) {
        ok=1;
        for (i=1;i<n;i++)
            if (s[i-1]>s[i]) {
                swap(s[i-1],s[i]);
                cnt++;
                ok=0;
            }
    }
    fout<<cnt;
    return 0;
}