#include <fstream>

using namespace std ;

const int NR = 10005 ;

ifstream f ("litere.in") ;
ofstream g ("litere.out") ;

int v [ 30 ] ;
int cnt ;

int main ()
{
    int p ; f >> p ;
    for ( unsigned i = 0 ; i < p ; ++ i )
    {
        char c ;f >> c ;
        v [ c - 'a' ] ++ ;
        for ( unsigned j = c - 'a' + 1 ; j < 26 ; ++ j )   cnt += v [ j ] ;
    }
    g << cnt ;
    return 0 ;
}