#include <fstream>
using namespace std;
ifstream f("litere.in");
ofstream g("litere.out");
int n,i,k,j,nr,c[100];
char s[10001];
int main()
{
    f >> n;
    for(i = 1; i <= n; ++i)
        f >> s[i];
    nr = 0;
    for(i = 1; i <= n; ++i)
    {
        k = s[i] - 97;
        ++c[k];
        for(j = k + 1; j <= 26; ++j)
            nr += c[j];
    }
    g << nr << '\n';
    return 0;
}