Den has two four-digit combination locks for protecting his bicycle from
thieves. Every evening he arms the bicycle antitheft alarm and fastens the
bicycle to a special stand with one of the locks. Den never uses the same
lock two evenings in a row. One night a thief tried to open the lock using
the code 0000. The alarm went off and the thief hurried away. The next
night the thief decided to try the code 0001, then 0002, and so on in ascending
order of the number.
Den never changes the codes of his locks. On the night when the thief came
for the first time the bicycle was fastened with the first lock.
The first line contains the combination that opens the first lock and the
second line contains the combination that opens the second lock. Both
combinations are strings consisting of four digits from 0 to 9.
Output “yes” if the thief will open the lock sooner or later and “no” otherwise.
Problem Author: Denis Mukhametianov
Problem Source: Ural Regional School Programming Contest 2011