#include <fstream>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");

long long ap[150], nr, n;
char c;

int main()
{
	int player_unu=0;

   in>>n;

   for (int i=1;i<=n;i++)
     {
         in>>c;

         ap[c]++;
         for (int j=c+1;j<='z';j++)
          nr+=ap[j];
     }
    out<<nr;

   return player_unu;
}