Задачі
A Famous Grid
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 in 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.
Вхідні дані
Each test case is described by a line of input containing two nonprime integer 1 ≤ x, y ≤ 10000.
Вихідні дані
For each test case, display its case number followed by the length of the shortest path or "impossible" (without quotes) in one line.
Приклад
Вхідні дані #1
1 4 9 32 10 12
Вихідні дані #1
Case 1: 1 Case 2: 7 Case 3: impossible