#include <fstream>

using namespace std;
ifstream cin("litere.in");
ofstream cout("litere.out");
string x ;
int v[ 100001 ];
int n ;
int main()
{
    cin >> n ;
    cin >> x;
    for ( int i = 0 ; i <n  ; i ++ )
    {
        v [ i + 1] = ( x[ i ] - 'a' );
    }

    bool sortat = false;

    int swaps = 0 ;
    while ( sortat == false )
    {
        sortat = true ;

        for( int i = 1; i < n ; i ++  )
        {
            if ( v [ i ] > v[ i + 1] )
            {
                swap ( v[ i ] , v[ i + 1 ] );
                swaps ++;
                sortat = false;
            }
        }


    }
    cout << swaps << '\n';
    return 0;
}