Billboard#3302
Once, an ACMer was driving down the highway. The road was so flat, straight for many miles: no potholes, no manholes, not even a turn for variety—boring, in a word. Out of boredom, the ACMer began to look at the billboards along and above the road. One billboard interested him so much that he wanted to get a better look at it, but without a board computer in his head, it's hard for him to figure out where to stop so that the billboard occupies the largest viewing angle.
For convenience, let's consider the billboard to be a segment on a plane, and the road as the -axis. The coordinates x_1, y_1, x_2, y_2 of the billboard's endpoints are given in four lines. All numbers are integers between and . The endpoints of the billboard are not the same.
Output a single number with decimal places — the size in radians of the largest possible viewing angle of the given billboard from the road.
Example 1