input: Write a python function to calculate the sum of all integers between two given numbers a and b (inclusive).
  assert calculateSum(1, 10) == 55
  assert calculateSum(5, 5) == 5
  assert calculateSum(1, 100) == 5050
  assert calculateSum(10, 20) == 165
output: def calculateSum(a, b):
      return sum(range(a, b + 1))