#include <iostream>
#include <fstream>
#include <string>
 using namespace std;
 ifstream fi("litere.in");
 ofstream  fo("litere.out");
int n,i,k=0;
char j;
char s[10000];
int frecv[26];
void test() {
     for (i=0; i<n; i++){
         for (j='a'; j<='z'; j++){
            if ((j > s[i]))
                          k+=frecv[j-'a'];}
         frecv[s[i]-'a']++;
         }                    
     }                       
int main() { 
fi >> n;
fi >> s;
test();
fo << k;

fi.close();
fo.close();
  return 0;
}