#include <fstream>
#include <algorithm>

using namespace std;

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

int n, nrInv, temp, j;
char c[10000];

int main()
{
    in >> n;
    for(int i = 0; i < n; i ++){
        in >> c[i];
        j = i;
        while (j > 0 && c[j] < c[j - 1]){
            nrInv ++;
            temp = c[j];
            c[j] = c[j-1];
            c[j-1] = temp;
            j --;
        }
    }
    out << nrInv;
    
    return 0;
}