input: Write a python function to add two complex numbers using a class.
  assert Complex(1, 2).add(Complex(3, 4)).real == 4
  assert Complex(1, 2).add(Complex(3, 4)).imag == 6
  assert Complex(-1, -2).add(Complex(3, 4)).real == 2
  assert Complex(-1, -2).add(Complex(3, 4)).imag == 2
output: class Complex:
      def __init__(self, real, imag):
          self.real = real
          self.imag = imag
          
      def add(self, other):
          return Complex(self.real + other.real, self.imag + other.imag)