#include<fstream>
using namespace std;
int n;
char s[10005];
int lit[10005],frecventa[10005];
long long suma;
int main()
{
  ifstream fin("litere.in");
  ofstream fout("litere.out");
  fin>>n;
  fin>>s;
  int i,j,su=0;
  for(i=0;s[i]!=0;i++)
  { 
   lit[s[i]]++;
   for(j=s[i]+1;j<=122;j++)  
      suma+=lit[j];
   }
    //if(lit[s[i]]==0)
      //lit[s[i]]++;
    fout<<suma<<" ";
    //suma+=su;
    //}  
   return 0;
}