#! /usr/bin/python
import sys
import math
x=float(sys.argv[1])
guess=42 # I want a +ve root, so seed is +ve
i=0
while guess*guess!=x and i<20:
# The iteration check is a must as many of the square-roots
# are irrational. The algorithm is quadratically convergent.
# ie. number of correct digits of the approximation doubles
# with each iteration. So a limit of 20 is pretty good.
guess = (guess+x/guess)/2
i+=1
# print \'guess=%f\\titer=%d\' % (guess,i)
print guess