class Solution:
def missingNumber(self, nums: List[int]) -> int:
start = 0
end = len(nums) - 1
if nums[0] != 0:
return 0
while start <= end:
mid = start + ((end-start)>>1)
if nums[mid] == nums[mid - 1] + 2:
return mid
elif nums[mid] == mid:
start = mid + 1
elif nums[mid] == mid + 1:
end = mid
return start