#include <fstream>

using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,nr,s;
char v[10001];
int b[10001];

int main()
{
    fin>>n;
    for(int i=1; i<=n; i++)
    {
        fin>>v[i];
        b[i]=int(v[i]);
    }
    /*do
    {
        s=1;
        for(int i=0;i<=n-1;i++)
        {
            if(b[i]>b[i+1])
            {
                int aux=b[i];
                b[i]=b[i+1];
                b[i+1]=aux;
                s=0;
                nr++;
            }
        }
    }while(!s);*/
    for(int i = 1 ; i <= n ; i ++)
    {
        int p = i;
        while(p > 0 && b[p] < b[p-1])
        {
            int aux = b[p];
            b[p] = b[p-1];
            b[p-1] = aux;
            p --;
            nr++;
        }
    }
    fout<<nr;
    return 0;
}