#include <fstream>

using namespace std;

ifstream fin ("litere.in");
ofstream fout("litere.out");

int n, mutari, cnt;
char sir[10001];

int main()
{
    fin >> n;
    for(int i = 1; i <= n; i++)
        fin >> sir[i];
    for(int i = 2; i <= n; i++)
    {
        cnt = i - 1;
        while(sir[cnt + 1] < sir[cnt])
        {
            swap(sir[cnt + 1], sir[cnt]);
            mutari++;
            cnt--;
        }
    }
    fout << mutari;
}