from math import pi, sqrt

def adist_term(xi1, xi, i):
    return (-1)**(i+1) * ( (1+sqrt(xi1**2 + xi**2)) / 2*pi )

def adist_t4t5(a, b):
    x1, x2 = a, b
    x3 = adist_term(x1, x2, 2)
    x4 = adist_term(x2, x3, 3)
    x5 = adist_term(x3, x4, 4)
    return round(x4+x5, 4)