Problem:
Score : 300 points

Problem Statement

You are given a grid of squares with H horizontal rows and W vertical columns, where each square is painted white or black.
HW characters from A_{11} to A_{HW} represent the colors of the squares.
A_{ij} is # if the square at the i-th row from the top and the j-th column from the left is black, and A_{ij} is . if that square is white.

We will repeatedly perform the following operation until all the squares are black:

Every white square that shares a side with a black square, becomes black.

Find the number of operations that will be performed.
The initial grid has at least one black square.

Constraints

1 \leq H,W \leq 1000

A_{ij} is # or ..

The given grid has at least one black square.

Input

Input is given from Standard Input in the following format:

H W
A_{11}A_{12}...A_{1W}
:
A_{H1}A_{H2}...A_{HW}

Output

Print the number of operations that will be performed.

Sample Input 1

3 3
...
.#.
...

Sample Output 1

2

After one operation, all but the corners of the grid will be black. After one more operation, all the squares will be black.

Sample Input 2

6 6
..#..#
......
#..#..
......
.#....
....#.

Sample Output 2

3

Solution in Python (3.8.2) (judge verdict: Wrong Answer)

h,w = map(int,input().split())
L = ["#" + input() + "#" for i in range(h)]
L = ["#"*(w+2)] + L + ["#"*(w+2)]
d = [["#"]+[0]*w + ["#"] for i in range(h)]
d = [["#"]*(w+2)] + d + [["#"]*(w+2)]
print(L,d)
li =((1,0),(0,1),(-1,0),(0,-1))

cnt = 0
while True:#not all(d[j][i] == "#" for j in range(1,h+1) for i in range(1,w+1)):
    for p in range(1,h):
        for q in range(1,w):
            if L[p][q] == "#":
                #print(p,q)
                d[p][q] = "#"
                #print(d)
                for x,y in li:
                    if L[p+x][q+y] == ".":
                        d[p+x][q+y] = "#"
    cnt +=1
    flag = False
    for j in range(1,h):
        for i in range(1,w):
            if d[j][i] == "#":
                flag = True
            else:
                flag = False
                break
    if flag == True:
        break
print(cnt)