Trying to solve it always leads to a contradiction:
(I have done the first step and already know that: navznyf ner ylvat)
Rry vf sbeprq vagb pryy 1 ol Qbt + Obbx. Bjy vf sbeprq vagb pryy 7 (fvapr pbyhza 2, ohg abg ebj 1 ohg nobir lrgv). Juvpu sbeprf Znyyrg vagb pryy 6 (fvapr qbt unf gb or va ebj 1 (sebz rry) naq qbt naq znyyrg pna'g or va fnzr ebj, naq znyyrg unf gb or orsber bjy) juvpu sbeprf Qvr vagb pryy 4 (fvapr unf gb or orsber bjy naq unf gb or va pbyhza 1 be 4). Sebz rry jr xabj gung ebj 2 vf gur bar jvgu gur 5 abgrf, fb ebj 1 bayl unf 4 abgrf, zrnavat pryy 3 vf Ubhfr naq pryy 2 vf qbt. Naq abj ebj 1 vf qbar ohg vg unf 2 navznyf jura gung pbagenqvpgf gur enoovg (fvapr "gurer ner gjb navznyf va gur svefg ebj" fubhyq or n yvr).
What am I missing?