#include<fstream>
#include<cstring>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int main(){
    //aflam signatura
    int i,j,n,inversiuni=0;
    char s[10000];
    fin>>n;
    fin.get();
    fin.getline(s,n+1);
    for(i=0;s[i]!=0;i++){
        for(j=i+1;s[j]!=0;j++) if(s[i]>s[j]) inversiuni++;
    }
    fout<<inversiuni;

}