You are provided with the kernels of six popular convolution filters. Which of these filters will detect only vertical edges?

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