type sir=array[1..10000] of char;
var x:sir;
    n,i,nr:integer;
    f,g:text;
    aux:char;
function ordo(x:sir; a:integer):boolean;
var i:integer;
begin
     ordo:=true;
     for i:=1 to a-1 do if x[i]>x[i+1] then
     begin
          ordo:=false;
          exit;
     end;
end;
begin
     assign(f,'litere.in'); reset(f);
     assign(g,'litere.out'); rewrite(G);
     readln(f,n);   nr:=0;
     for i:=1 to n do read(f,x[i]);
     while not ordo(x,n) do
           for i:=1 to n-1 do
               if x[i]>x[i+1] then
               begin
                    aux:=x[i];
                    x[i]:=x[i+1];
                    x[i+1]:=aux;
                    inc(nr);
               end;
     writeln(g,nr);
     close(g);
end.