input: Write a python function to calculate the number of integers divisible by 7 in a given range.
  assert calculate_divisible_by_7(18, 48) == 5
  assert calculate_divisible_by_7(1, 7) == 1
  assert calculate_divisible_by_7(14, 21) == 2
output: def calculate_divisible_by_7(start, end):
      count = 0
      for i in range(start, end + 1):
          if i % 7 == 0:
              count += 1
      return count