program pascal;
var f,g:text;
    n,i,j,k:longint; nr:int64;
    v:ansistring;
    ok:boolean; aux,c:char;

  procedure citire;
  begin
   readln(f,n);
   read(f,v);
  end;

  procedure form;
  begin
 nr:=0;
 i:=2;
 while i<=n do
 begin
 ok:=false;
 aux:=v[i];
 k:=i-1;
 while v[i]<v[k] do
         begin
                 nr:=nr+1;
                 ok:=true;
                 k:=k-1;
         end;
 if ok then
                 begin
                  k:=k+1;
                  delete(v,i,1);
                  insert(aux,v,k);
                 end;
 i:=i+1;
 end;

 write(g,nr);

  end;

begin
 assign(f,'litere.in'); reset(f);
 assign(g,'litere.out'); rewrite(g);
  citire;
  form;
 close(f);
 close(g);
end.