var v:array[1..10000]of char;
   n,k,l,i:integer;
   c:char;
   f,g:text;
   q:boolean;
begin
assign(f,'litere.in');
reset(f);
readln(f,n);
for i:=1 to n do
read(f,v[i]);
close(f);
q:=false;
k:=0;
while not q do
begin
  l:=0;
  for i:=1 to n-1 do
      if ord(v[i])>ord(v[i+1]) then begin
                          inc(k);
                          c:=v[i];
                          v[i]:=v[i+1];
                          v[i+1]:=c;
                          end;
    for i :=1 to n-1 do
    if ord(v[i])>ord(v[i+1]) then begin l:=l+1; break; end;
    if l=0 then q:=true;
   end;
assign(g,'litere.out');
rewrite(g);
writeln(g,k);
close(g);
end.