var
  i,j,k:char;
  s:longint;
begin
  s:=0;
  for i:='a' to 'z' do
  for j:='a' to 'z' do
  for k:='a' to 'z' do
  begin
    write(i);inc(s);if(s>=1000000)then begin writeln;exit;end;
    write(j);inc(s);if(s>=1000000)then begin writeln;exit;end;
    write(k);inc(s);if(s>=1000000)then begin writeln;exit;end;
  end;
end.

sorry,i know what's wrong with me!i've Ac!!!!!!!!!
if you want to know how to slove it,please send e-mail to me!
My e-mail is whyzhc@sohu.com

> var
>   i,j,k:char;
>   s:longint;
> begin
>   s:=0;
>   for i:='a' to 'z' do
>   for j:='a' to 'z' do
>   for k:='a' to 'z' do
>   begin
>     write(i);inc(s);if(s>=1000000)then begin writeln;exit;end;
>     write(j);inc(s);if(s>=1000000)then begin writeln;exit;end;
>     write(k);inc(s);if(s>=1000000)then begin writeln;exit;end;
>   end;
> end.