#include <fstream>
#include <cstring>
using namespace std;
//Sortare prin Interschimbare

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

int n,i,h,j,cont=0;
char sir[1001];
int main()
{
    cin>>n;
    cin>>sir;
    for(i=1; i<n; i++)
        for(j=0; j<i; j++)
            if(sir[i]<sir[j])
               cont++;

        cout<<cont;

    return 0;
}