#!/usr/bin/python3
#The atan() method returns the arc tangent of x, in radians.
#atan(x)
import math

a = -0.8
b = math.atan(a)
print(b)
print ("atan(0.64) : ", math.atan(0.64))
print ("atan(0) : ", math.atan(0))
print ("atan(10) : ", math.atan(10))
print ("atan(-1) : ", math.atan(-1))
print ("atan(1) : ", math.atan(1))