anak tangga yg sulung

if by any chance u were confused while reading the text,kindly proceed to the diagram

"as the monster slowly crept up the stairs,the protagonist(put ur name here if u like) was paralyzed by looking into the monster sickly green eye.staring stared stiff,he watched in fear as the monster was four steps away from him and grasped for his feet.." an excerpt from some bogus horror book that i made up.

so..
in the imaginary excerpt,the hero was going to be eaten.
usually when people read something,they usually imagine it up.
certain things,such as the background.in this case the stairs.
howeva james,
when i read it,there's a conflict in it.
see,the monster reach its hand when it was four steps away
four steps.
4 anak tangga .

the question is,how do u determine it?

there was once when i counted how many anak tangga there were on this certain flight of stairs.
he step on the anak tangga 1 by 1 and started counting.
but i took two steps at a time and started counting.so if i missed counting,it will give a difference of 2,compared to my friend.

however,he counted 29steps,i got 30.difference is 1.
so we recounted. 29 and 30.
it is impossible for difference to be 1, since the logic is when i took 2 steps and ended my steps directly at the top of the stairs,then the number of anak tangga must be a multiple of two.
it is improbable,though not possible,that i miscounted.so if i put either of my foot directly at the top of the stairs,and i were to miscount,the difference to my friend counting would still be a multiple of two.

apparently the problem was we ended the count differently.
my last anak tangga is his second last.

here's a diagram to simplify.(AT stands for anak tangga)

so which one is the right definition?
A or B?
kindly vote on the left,thank you

note:
1. there are significances in determining this.
2. the terms landing, flight, steps, and anak tangga have different meaning.to avoid misinterpretation i had to use anak tangga to convey my meaning.