problem with complex number

[jodrickcolina]

I have a problem when I wanna work with complex number in python 3, the problem is that I do not know how to convert a string to "complex" when I save a complex number in a variable, for example, the next code:

import math
import cmath
print("calculo de las constantes generalizadas")
Z=input("ingrese el parametro Z ohm/km: ")
Y=input("ingrese el parametro Y siemen/km: ")
g=cmath.sqrt(Z*Y)
print(g)

In Z, I put for example: 5+5j
In Y, I put 2j

and this is the problem:

Error:
Traceback (most recent call last):
  File "C:/Users/Usuario/AppData/Local/Programs/Python/Python37-32/test.py", line 6, in <module>
  g=cmath.sqrt(Z*Y)
TypeError: can't multiply sequence by non-int of type 'str'

I need to work with complex number but I don't know how to covert str to "complex"