#include <fstream>

using namespace std;

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

int n,i,j;
char c[10001];
int rez;

int main()
{
    f>>n;
    for (i=1;i<=n;i++)
    {
        f>>c[i];
        for (j=1;j<i;j++)
            if (int(c[j]) > int(c[i]))
                rez++;
    }

    g<<rez;

    return 0;
}