Beryland Crab
Upon discovering Krylandia's plans to tap into the main carrot juice pipeline, Berlandia's top scientists quickly decided to take action. To support their official complaints to various largely ineffective authorities, they built a specialized robot—an underwater crab. The primary mission of the "Berlandian Crab," which travels along the pipeline, is to monitor the Krylandian coastal area. If it detects any underwater construction activity, it must immediately alert the Berlandian government.
Monitoring the entire length of the pipeline (as depicted in the figure) would be economically unfeasible and, given the crab's current slow speed, it might miss the start or end of construction activities. Therefore, the decision was made to focus on a specific section of the pipeline to observe the Krylandian coastal zone.
The most likely connection point has been identified as a straight segment of the shore. Before deploying their industrial espionage tool, the Berlandian scientists want to know: "What is the maximum angle at which the 'Berlandian Crab' can view the specified coastal section?"
For calculation simplicity, assume the main pipeline is straight and aligned along the OX axis (we can position this axis as we please!). The pipeline does not intersect or even touch any part of Krylandian territory.
Input
The input consists of one or more lines containing four integers: X_1, Y_1, X_2, Y_2, which represent the coordinates of the endpoints of the most vulnerable section for connection. All coordinates are integers with absolute values not exceeding 1000.
Output
Output a single number representing the desired angle in radians, with a precision of at least 6 decimal places.