This tests helped me with WA3, WA5 and WA10, but now I'm stuck at test 20. Any hints?

4 9
010000010
111010111
101111101
000101000
answer: 9

4 5
11000
01100
00110
00011
answer: 4

5 5
11100
11110
11111
01111
00111
answer: 3

4 9
100111100
100100100
100100100
111100111
answer: 6

This helped with test 20, now WA31 to overcome!

4 5
00100
01110
01010
11011
answer: 5