#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
char c[10001], aux;
int sw, k, i, n;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>c[i];
    do
    {
        sw=0;
        for(i=1;i<n;i++)
            if(c[i]>c[i+1])
        {
            aux=c[i];
            c[i]=c[i+1];
            c[i+1]=aux;
            k++;
            sw=1;
        }
    } while(sw);
    fout<<k;
    return 0;
}