Program p1;
var fi,fo : text;
    i,k,j,n :longint;
    a : array[1..10000] of char;

begin
    assign(fi,'litere.in'); reset(fi); readln(fi,n);
    assign(fo,'litere.out'); rewrite(fo);
    read(fi,a);

    for i:=1 to n do
        for j:=i+1 to n do if a[i]>a[j] then k:=k+1;

    writeln(fo,k);

    close(fi); close(fo);
end.