P11271 "Diligent-OI R1 A" DlgtPattern
Description
A cup is placed in an opaque box. The base of the cup can be regarded as a circle. The box can be regarded as a rectangular cuboid, and its thickness can be ignored.
Now place the bottom face of the box in a 2D Cartesian coordinate system. Its four vertices are at $(0,0)$, $(x,0)$, $(0,y)$, and $(x,y)$.
You only know that the center of the circular base of the cup is at $(p,q)$. What is the maximum possible radius of the cup’s base?
Input Format
Only one line is given, containing four integers $x,y,p,q$.
Output Format
Output only one number: the maximum possible radius of the cup’s base.
Explanation/Hint
#### Explanation for Sample #1
The situation where the cup radius is the largest is shown in the figure below.
#### Constraints
For $100\%$ of the testdata, $0