#include <fstream>

using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
int main()
{
    int n;
    in>>n;
    char letters[10001];
    for (int i=0; i<n; i++)
    {
        in>>letters[i];
    }
    int swaps=0;
    bool sorted=0;
    while(sorted==0)
    {
        sorted=1;
        for(int i=0; i<n-1; i++)
        {
            if(letters[i]>letters[i+1])
            {
                char sw=letters[i];
                letters[i]=letters[i+1];
                letters[i+1]=sw;
                swaps++;
                sorted=0;
            }
        }
    }
    out<<swaps;
}