from math import pi, sqrt

def kpi_next_term(xi1, xi, k):
    return k*pi / (1+sqrt(xi1**2 + xi**2))

def kpi_term5(x1, x2, k):
    x3 = kpi_next_term(x1, x2, k)
    x4 = kpi_next_term(x2, x3, k)
    x5 = kpi_next_term(x3, x4, k)
    return round(x5, 4)