Problem: 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.

Examples

Input

3 3
...
.#.
...


Output

2


Input

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


Output

3

Solution (in PYTHON3):

Solution:
from collections import deque

h, w = map(int, input().split())
a = [list(input()) for _ in range(h)]

d = [[-1] * w for _ in range(h)]
que = deque()
for i in range(h):
    for j in range(w):
        if a[i][j] == '#':
            que.append((j, i))
            d[i][j] = 0

dxdy = [(1, 0), (-1, 0), (0, 1), (0, -1)]

ans = 0
while que:
    x, y = que.popleft()
    for dx, dy in dxdy:
        nx = x + dx
        ny = y + dy
        if 0 <= nx < w and 0 <= ny < h and d[ny][nx] == -1:
            que.append((nx, ny))
            d[ny][nx] = d[y][x] + 1
            ans = max(ans, d[ny][nx])

print(ans)