到底 とうてい
tōtei

Adverb

1. (cannot) possibly; (not) by any means; (not) at all; utterly; absolutely

Usually Written in Kana
あなたの はなし到底 とうてい真実 しんじつだと おもえない。
anatano hanashiwa tōtē shinjitsudato omoenai.
I can't possibly think your story is true.