Finding a Perfect Square

You are given a table A with N rows and M columns. Each cell contains a single digit.

Yeondu wants to choose one or more distinct cells. When the chosen cells are listed in the order they are picked, their row numbers must form an arithmetic sequence, and their column numbers must also form an arithmetic sequence. Concatenating the digits written in the chosen cells, in the order they were picked, forms a single integer.

Find the largest perfect square among the integers Yeondu can form. A perfect square is a number obtained by squaring some integer.

The first line contains two integers N and M separated by a space.

Each of the next N lines contains one row of the table, from row 1 to row N in order. On each line, the digits of that row are given from column 1 to column M with no spaces between them.

Print the largest perfect square Yeondu can form on the first line. If no perfect square can be formed, print -1.

• 1 ≤ N, M ≤ 9
• Each digit written in the table is between 0 and 9, inclusive.