The current positive numbers should increase like i.If 1 was missed, num != i and num + 1 != i, it will return 1. After the num in nums be >= 0 firstly, the num should be 0 or 1, just num == 1, i++ or num + 1 == i, the i will increase normally. if num not equals i, it will return the missing positive num. My English is not good, please forgive me.

```
class Solution(object):
def firstMissingPositive(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
nums.sort()
f = i = 1
for index, num in enumerate(nums):
if num > 0 and f:
f = 0
if not f:
if num == i:
i += 1
elif num + 1 == i:
continue
else:
return i
return i
```