It is said in the situation that
1 <= |X1|, |Y1|, |X2|, |Y2| <= 30000.

But the Sample Input provided shows, that Y1=0 and X2=0 are allowed.

So, Sample Input contradicts the problem situation, doesn't it?

I think that your observation is right. It is bad description of problem.

I think authors wants say, that
0 ≤ |X1|, |Y1|, |X2|, |Y2| ≤ 30000,
but |X1| + |Y1| > 0  and |X2| + |Y2| > 0.

I.E. (X1, Y1) != (0, 0)  and  (X2, Y2) != 0.