While debugging a program, Mirko noticed that a bug may be linked with the existence of so-called square killers in the program memory. The program memory is a matrix of \(R\) rows and \(C\) columns consisting only of zeroes and ones. A square killer is a square submatrix, consisting of more than one character, that looks exactly the same when rotated \(180\) degrees.

For example, the following matrix contains \(3\) square killers, of sizes \(3\), \(2\) and \(2\):

101010
111001
101001

Mirko is wondering if there is a connection between the size of the largest square killer and the bug. Help Mirko by writing a program that, given the layout of the memory, outputs the size of the largest square killer. The size of a square killer is the number of rows (equivalently, columns) it consists of.

The first line contains two integers \(R\) and \(C\), both smaller than or equal to \(100\).

The next \(R\) lines each contain \(C\) characters (0 or 1) with no spaces.

Output the size of the largest square killer on a single line, or output -1 if there are no square killers.

riseoj 작성

출처 COCI 2006/2007 Contest 1