I guess all devices are unique. I've passed test 10 when i've passed this:

q a 1
q b 2
q c 3
q d 4
q e 5
q f 6

If you're getting WA #10, better try this test where prices aren't already sorted:
a 1 6
b 2 4
c 3 5
d 4 3
e 5 1
f 6 2
Correct answer is "5", got AC after this test passed.