text: #!/usr/bin/env python3
  # -*- coding: utf-8 -*-
  
  import math
  import sys
  
  EULER = 0.5772156649015328606
  EPS = 1e-10
  
  if __name__ == '__main__':
      x = float(input("Value of x? "))
      if x == 0:
          print("Illegal value of x", file=sys.stderr)
          exit(1)
  
      a = (-x**2)/4
      S, n = a, 1
  
      while math.fabs(a) > EPS:
          a *= (-(x**2*2*n)/(2*(n+1)**2))
          S += a
          n += 1
  
      print(f"Сi({x}) = {EULER + math.log(math.fabs(x)) + S}")
  