I spend 3 hours searching to find the bug, but i found nothing, pls help me solve it...

i had the same problem, but after realising that i might have made a mistake somewhere, i tried test case someone else already posted:
5
0 0
0 2
1 1
2 0
2 2

so, when i "fixed" my program, now i have WA#4 instead of WA#7 :P