# Enter your code here. Read input from STDIN. Print output to STDOUT
import math

l_AB = input()
l_BC = input()
l_AC = (((l_AB**2)+(l_BC**2))**.5)

l_MC = (l_AC/2)
l_MB = (((l_BC**2)-(l_MC**2))**.5)

a_MBC_p = l_MC/l_BC

a_MBC = math.acos(a_MBC_p)

print(a_MBC)