# Task
 You're given a two-dimensional array of integers `matrix`. Your task is to determine the smallest non-negative integer that is not present in this array.
# Input/Output
 - `[input]` 2D integer array `matrix`
  A non-empty rectangular matrix. 
 `1 ≤ matrix.length ≤ 10`
 `1 ≤ matrix[0].length ≤ 10`
 - `[output]` an integer
  The smallest non-negative integer that is not present in matrix.
# Example
 For 
 ```
 matrix = [
 [0, 2],
 [5, 1]]```
 the result should be `3`
 0,1,2,`(3)`...5
from itertools import count

def smallest_integer(matrix):
    nums = {n for row in matrix for n in row}
    for i in count():
        if i not in nums:
            return i
from itertools import count

def smallest_integer(matrix):
    nums = {n for row in matrix for n in row}
    for i in count():
        if i not in nums:
            return i