CJam, 9 bytes

CJam has mQ, but unfortunately it trunctuates to an integer ... Another port of Lyxal's answer.

q~2 .5#/i

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Explanation

q~ e# Take input & evaluate
 2 e# Take 2 to the power of ...
 .5# e# ... 0.5 (equal to square root)
 / e# Divide the input by it
 i e# Convert to integer