SPIRALGR  A Famous Grid
Mr. B has recently discovered the grid named "spiral grid". Construct the grid like the following figure. (The grid is actually infinite. The figure is only a small part of it.)
Considering traveling around it, you are free to any cell containing a composite number or 1, but traveling to any cell containing a prime number is disallowed. You can travel up, down, left or right, but not diagonally. Write a program to find the length of the shortest path between pairs of nonprime numbers, or report it's impossible.
Input
Each test case is described by a line of input containing two nonprime integer 1 <=x, y<=10,000.
Output
For each test case display its case number followed by the length of the shortest path or impossible in one line.
Example
Input: 1 4 9 32 10 12 Output: Case 1: 1 Case 2: 7 Case 3: impossible
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navneet_01:
20201013 09:19:57
can anyone give me a hint? 

Bojan Rosko:
20130415 18:20:15
The spiral is infinite. So, even though x, y <10000 , the output can theoretically be larger than 200 , am I right ? You get numbers from grid 100 x 100, but the path can get out of that grid because the spiral is infinite ?


PetarV:
20130411 06:39:33
It is supposed to keep reading the test cases and solving them until it covers all of them. (there are finitely many test cases in the test input) Last edit: 20130411 06:42:30 

Aleksandar BorzanoviĆ¦:
20130409 19:12:52
is the program supposed to stop after each test case, or just spin in an infinite loop, solving cases in real time? 
Added by:  Fudan University Problem Setters 
Date:  20120525 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 
Resource:  ACM/ICPC World Finals 2012  Dressing Rehearsal Contest, also used in FDU Local Contest 2012 