AOJ 2741 Invisible

Solved Users (link to submissions)
amano
Aquarius
arrows
arsenic28
arukuka
asi1024
beet
c7c7
chuo2015
clavis1107
DAyama
dohatsu
E869120
ei1333
femto16
ferin
gasin
gru
haji149
homesentinel
id
imulan
is0384er
ixmel
jakenu0x5e
jin_matakich
joisino
kopricky
kurenai3110
latte0119
leaf1415
Maekwa_Miku
moti
mtsd
naoto172
nokoTaro
pachicobue
paruki
primenumber
qras
rian_tkb
roto_37
s1230146
s1230149
s1230151
s16ti012
shinya_kato
soraziro222
suibaka
syl659
takoshi
Tsuta_J
tyage
ukuku09
vjudge1
vjudge2
vjudge3
vjudge4
vjudge5
Yang33
yurahuna