input: Write a python function to find the missing number in a list of consecutive numbers.
  assert find_missing_number([1, 2, 4, 6, 7, 8]) == 3
  assert find_missing_number([10, 11, 12, 14, 15]) == 13
  assert find_missing_number([5, 6, 7, 9, 10]) == 8
output: def find_missing_number(nums):
      n = len(nums) + 1
      total_sum = n * (nums[0] + nums[-1]) // 2
      actual_sum = sum(nums)
      return total_sum - actual_sum