#include <fstream>
#include <string>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
char  sir[10001];
int main()
{
    int n, i, contor = 0;
    in >> n;
    for(i=1;i<=n;i++){
        in >> sir[i];
        int j = i;
        while(j>1){
            if(sir[i]<sir[j-1]) contor++;
            j--;
        }
    }
    out << contor;
    return 0;
}