#include <fstream>
#include <iostream>

using namespace std;

const int NMAX = 1e4 ;
char v [ NMAX + 5 ] ;
int f [ 30 ] ;

int main()
{
    ifstream in ( "litere.in" ) ;
    ofstream out ( "litere.out" ) ;

    int n , i , j , ans = 0 ;

    in >> n ;

    for ( i = 1 ; i <= n ; ++ i )
        in >> v [ i ] ;

    for ( i = n ; i >= 1 ; -- i )
    {
        ++ f [ v [ i ] - 'a' + 1 ] ;

        for ( j = v [ i ] - 'a' ; j >= 1 ; -- j )
            ans += f [ j ] ;
    }

    out << ans ;
    return 0;
}