#include<iostream>
#include<fstream>

char aux;
using namespace std;

int n,ss=0;
char a[10001];


void contor()
{
    int i,j;

for(j=0;j<n;j++)
for(i=0;i<n-1;i++)
{
    if(a[i+1]<a[i])
        {
            aux=a[i+1];
            a[i+1]=a[i];
            a[i]=aux;
            ss++;
        }


}

}



int main()
{
    ifstream f ("litere.in");
    ofstream o ("litere.out");
    f>>n;
    f.get();
    f.get(a,n+1);
 contor();
int i;
//for(i=0;i<n;i++)
  //  cout<<a[i]<<" ";
o<<ss;



return 0;}