from collections import deque
import sys
input=sys.stdin.readline
h,w=map(int,input().split())
g=[input() for _ in range(h)]
d=[[-1]*w for _ in range(h)]
dy=[1,1,1,0,0,-1,-1,-1]
dx=[1,0,-1,1,-1,1,0,-1]
for y in range(h):
    for x in range(w):
        if g[y][x]=='.':
            d[y][x]=0
            continue
        sea=False
        for i in range(8):
            ny=y+dy[i]
            nx=x+dx[i]
            if not (0<=ny<h and 0<=nx<w):
                sea=True
                break
            if g[ny][nx]=='.':
                sea=True
                break
        if sea:
            d[y][x]=1
q=deque()
for i in range(h):
    for j in range(w):
        if g[i][j]=='.':
            continue
        if d[i][j]==1:
            q.append((i,j))
while q:
    y,x=q.popleft()
    for i in range(8):
        ny=y+dy[i];nx=x+dx[i]
        if not(0<=ny<h and 0<=nx<w):
            continue
        if g[ny][nx]=='.':
            continue
        if d[ny][nx]==-1:
            d[ny][nx]=d[y][x]+1
            q.append((ny,nx))
ans=0
for i in range(h):
    for j in range(w):
        if d[i][j]>ans:
            ans=d[i][j]
print(ans)