#include<fstream>
#include<cstring>
using namespace std;

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

const int NMAX=10005;

int n,sumepart[NMAX],aux[NMAX];
char s[NMAX],cas[NMAX];
long long sum;

int main()
{
    int i,nr,pozstart=1,deja=0;
    char c;
    fin>>n;
    fin>>(s+1);
    strcpy((cas+1),(s+1));
    for (c='a';c<='z';c++)
        {
            nr=0;
            for (i=1;i<=n;i++)
                if (cas[i]==c)
                    {
                        nr++;
                        deja++;
                        sum+=i-deja;
                    }
            for (i=pozstart;i<=pozstart+nr-1;i++) cas[i]=c;
            pozstart+=nr;
            nr=pozstart;
            for (i=1;i<=n;i++) if (s[i]>c) cas[nr++]=s[i];
        }
    fout<<sum<<"\n";
    return 0;
}