input: Write a function to read an array of integers and calculate their sum. Implement the function as follows:
  
  def calculate_sum(arr):
      sum = 0
  
      for i in arr:
          sum += i
  
      return sum
  
  input_array = [1, 3, 5, 7]
  
  assert calculate_sum(input_array) == 16
  assert calculate_sum([2, 4, 6]) == 12
  assert calculate_sum([]) == 0
  assert calculate_sum([10, 20, 30, 40, 50]) == 150
  assert calculate_sum([-1, -2, -3]) == -6
output: def calculate_sum(arr):
      sum = 0
      for i in arr:
          sum += i
      return sum