#CJam , 8 bytes
l_,mQ/N*
###Explanation
l e# Read line from input
_, e# Duplicate. Get length
mQ e# Integer square root
/ e# Split into pieces of that size
N* e# Join by newline. Implicitly display
CJam , 8 bytes
l_,mQ/N*
Explanation
l e# Read line from input
_, e# Duplicate. Get length
mQ e# Integer square root
/ e# Split into pieces of that size
N* e# Join by newline. Implicitly display
#CJam, 8 bytes
l_,mQ/N*
###Explanation
l e# Read line from input
_, e# Duplicate. Get length
mQ e# Integer square root
/ e# Split into pieces of that size
N* e# Join by newline. Implicitly display