#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin ("litere.in");
ofstream fout ("litere.out");
int n,i,j,k,g,h;
char s[10001];
int main()
{
    fin>>n;
    for (i=1; i<=n; i++)
        fin>>s[i];
    for (i=1; i<n; i++)
    {
        j=i+1;
        if (s[i]>s[j])
        {
            g=j;
            h=g-1;
            while (s[h]>s[g])
            {
                swap (s[h],s[g]);
                g--;
                h--;
                k++;
            }
        }
    }
    fout<<k;
    return 0;
}