var a:array[1..10000] of char;
    aux:char;
    nr,n,i,j,p:integer;
    f,g:text;
begin
assign(f,'litere.in');reset(f);
assign(g,'litere.out');rewrite(g);
readln(f,n);
for i:=1 to n do
    read(f,a[i]);
nr:=0;
for i:=1 to n do
    for j:=n downto i+1 do
        if a[j]<a[j-1] then begin
           aux:=a[j];a[j]:=a[j-1];a[j-1]:=aux;
           inc(nr);
        end;
writeln(g,nr);close(g);
end.