You are given a two-dimensional table (grid) A of N rows and M columns. Every cell contains a lowercase letter, one of 'a' - 'z'.

Let's call two cells of A adjacent, if they share a common side.

Let's call a set S of cells a connected region if the following three conditions are satisfied:

S is connected, i.e. every pair of cells in S can be reached from each other by moving along a path of adjacent cells of S.
All the letters written in the cells of S are the same.
It's impossible to extend it, i.e. there are no more cells of A, that can be added to S so that the first two conditions still hold.

Let's say, that a connected region S is completely inside another connected region T, if there's a cycle path of adjacent cells of T, such that all the cells of S are inside the contour (shape), formed by the cycle path.

Let's call a table acceptable if there is no connected region completely inside some other connected region. Your task is to determine whether the given table A is acceptable, and print \(\text{YES}\) or \(\text{NO}\) accordingly.

Input format

The first line contains one integer T denoting the number of test cases in the input.

The first line of each test case description contains two integers N and M denoting the number of rows and the number of columns in A respectively.

Each of the next N lines contains a string of M lowercase letters, each denoting one row of the table A.

Output format

For each test case, output the answer in a separate line. The answer is \(\text{YES}\) if the given table is acceptable, and \(\text{NO}\) otherwise.

Constraints

\(1 \le T \le 18\)
\(1 \le N \cdot M \le 10^6\) (it's multiplication, not a comma)
\(N \le M\).

Subtasks

Extra constraints	Points	Which tests
\(N \cdot M \le 100\)	30	1
no extra constraints	70	2