input: Write a python function to calculate the sum of a list of numbers.
  assert calculate_sum([1, 2, 3, 4, 5]) == 15
  assert calculate_sum([10, 20, 30, 40]) == 100
  assert calculate_sum([-1, -2, -3, -4]) == -10
output: def calculate_sum(numbers):
      return sum(numbers)