I've had some trouble solving this and I'm sure there are some tests
where ai>bi. How do I know? Well, I got a lot of WAs, so at some
point I inserted this into my code, where I read the data:
  if ai>bi then
     while 1=1 do writeln('Error!');
Guess what? I got Output Limit Exceeded instead of WA. So if you want
to get AC, you also have to ignore the lines where ai>bi.