```
class Solution(object):
def removeDuplicates(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
i = 0
while i < len(nums)-2:
if nums[i]==nums[i+2]: # because is sorted, this means nums[i],nums[i+1],nums[i+2] are equal
del nums[i+2]
elif nums[i] == nums[i+1]:
i = i+2
else:
i = i+1
return len(nums)
```