You are provided with the kernels of six popular convolution filters. Which of these filters will leave the image unchanged upon convolution?

Only enter the integer corresponding to the appropriate filter in the text box. Do not leave any leading or trailing spaces or newlines.

1

    0   0   0
    0   1   0
    0   0   0

2

    -1  -1  -1
    -1   8  -1
    -1  -1  -1

3

     0  -1   0
    -1   5  -1
     0  -1   0

4

    1/16    1/8     1/16
    1/8     1/4     1/8
    1/16    1/8     1/16  

5

    -1  0   1
    -2  0   2
    -1  0   1

6

    -1  -2  -1
     0   0   0
     1   2   1