#include <iostream>
#include <fstream>

using namespace std;
ifstream f("litere.in");
ofstream g("litere.out");

int n,i,a[10000],aux,sw,contor;
char cif;
int main()
{
    f>>n;
    for(i=0;i<n;i++)
    {
        f>>cif;
        a[i]=cif-'a';
    }
    do
    {
        sw=0;
        for(i=0;i<n-1;i++)
        {
            if(a[i]>a[i+1])
            {
                aux=a[i];
                a[i]=a[i+1];
                a[i+1]=aux;
                sw=1;
                contor++;
            }
        }
    }while (sw==1);
    g<<contor;
    return 0;
    f.close();
    g.close();
}