Buggy python submission (verdict: Time Limit Exceeded):
import queue
import copy

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = queue.Queue()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.put([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while not q.empty():
        x,y = q.get()
        if c[y][x-1] == '.':
            q.put([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.put([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.put([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.put([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)


Fixed submission:
from subprocess import call
call (('pypy3', '-c', """
from collections import deque

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = deque()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.append([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while q:
        x,y = q.popleft()
        if c[y][x-1] == '.':
            q.append([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.append([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.append([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.append([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)
"""))

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
import copy

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = deque()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.append([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while q:
        x,y = q.popleft()
        if c[y][x-1] == '.':
            q.append([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.append([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.append([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.append([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)


Fixed submission:
from subprocess import call
call (('pypy3', '-c', """
from collections import deque

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = deque()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.append([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while q:
        x,y = q.popleft()
        if c[y][x-1] == '.':
            q.append([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.append([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.append([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.append([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)
"""))

Buggy python submission (verdict: Time Limit Exceeded):
import queue
import copy

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = queue.Queue()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.put([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while not q.empty():
        x,y = q.get()
        if c[y][x-1] == '.':
            q.put([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.put([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.put([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.put([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)


Fixed submission:
from subprocess import call
call (('pypy3', '-c', """
from collections import deque

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = deque()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.append([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while q:
        x,y = q.popleft()
        if c[y][x-1] == '.':
            q.append([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.append([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.append([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.append([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)
"""))

Buggy python submission (verdict: Time Limit Exceeded):
import queue
import copy

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = queue.Queue()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.put([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while not q.empty():
        x,y = q.get()
        """
        if [x,y] == [gx,gy]:
            return ans[gy][gx]
        """
        if c[y][x-1] == '.':
            q.put([x-1,y])
            ans[y][x-1] = min(ans[y][x] + 1,ans[y][x-1])
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.put([x+1,y])
            ans[y][x+1] = min(ans[y][x] + 1,ans[y][x+1])
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.put([x,y-1])
            ans[y-1][x] = min(ans[y][x] + 1,ans[y-1][x])
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.put([x,y+1])
            ans[y+1][x] = min(ans[y][x] + 1,ans[y+1][x])
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)


Fixed submission:
from subprocess import call
call (('pypy3', '-c', """
from collections import deque

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = deque()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.append([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while q:
        x,y = q.popleft()
        if c[y][x-1] == '.':
            q.append([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.append([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.append([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.append([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)
"""))

Buggy python submission (verdict: Time Limit Exceeded):
import queue
import copy

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = [[0 for _ in range(W+2)]for i in range(H+2)]

for i in range(H):
    tmp = list('×'+input()+'×')
    c.append(tmp)

c.append(['×' for _ in range(W+2)])

def bfs(x,y):
    q.put([x,y])

    while not q.empty():
        x,y = q.get()

        if c[y][x-1] == '#':
            return ans[y][x] + 1
        if c[y][x+1] == '#':
            return ans[y][x] + 1
        if c[y-1][x] == '#':
            return ans[y][x] + 1
        if c[y+1][x] == '#':
            return ans[y][x] + 1

        if c[y][x-1] == '.':
            q.put([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '×'
        if c[y][x+1] == '.':
            q.put([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '×'
        if c[y-1][x] == '.':
            q.put([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '×'
        if c[y+1][x] == '.':
            q.put([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '×'

c_copy = copy.deepcopy(c)
ans_copy = copy.deepcopy(ans)
max_ans = 0
for i in range(1,H+1):
    for j in range(1,W+1):
        if c[i][j] == '.':
            q = queue.Queue()
            max_ans = max(bfs(j,i),max_ans)
            c = copy.deepcopy(c_copy)
            ans = copy.deepcopy(ans_copy)

print(max_ans)


Fixed submission:
from subprocess import call
call (('pypy3', '-c', """
from collections import deque

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = deque()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.append([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while q:
        x,y = q.popleft()
        if c[y][x-1] == '.':
            q.append([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.append([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.append([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.append([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)
"""))

Buggy python submission (verdict: Time Limit Exceeded):
import queue
import copy

H,W = map(int,input().split())
c =[]
c.append(['#' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
for _ in range(H):
    tmp = list('#'+input()+'#')
    ans_tmp = []
    for i in range(W+2):
        if tmp[i] == '#':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['#' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])
q = queue.Queue()

def bfs(x,y):
    global q
    global c
    global ans
    q.put([x,y])

    while not q.empty():
        x,y = q.get()
        """
        if [x,y] == [gx,gy]:
            return ans[gy][gx]
        """
        if c[y][x-1] == '.':
            q.put([x-1,y])
            ans[y][x-1] = min(ans[y][x] + 1,ans[y][x-1])
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.put([x+1,y])
            ans[y][x+1] = min(ans[y][x] + 1,ans[y][x+1])
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.put([x,y-1])
            ans[y-1][x] = min(ans[y][x] + 1,ans[y-1][x])
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.put([x,y+1])
            ans[y+1][x] = min(ans[y][x] + 1,ans[y+1][x])
            c[y+1][x] = '#'

c_copy = copy.deepcopy(c)

for i in range(1,H+1):
    for j in range(1,W+1):
        if c[i][j] == '#':
            c = copy.deepcopy(c_copy)
            bfs(i,j)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)

Fixed submission:
from subprocess import call
call (('pypy3', '-c', """
from collections import deque

H,W = map(int,input().split())
c =[]
c.append(['×' for _ in range(W+2)])
ans = []
ans.append([0 for _ in range(W+2)])
q = deque()
for i in range(H):
    tmp = list('×'+input()+'×')
    ans_tmp = []
    for j in range(W+2):
        if tmp[j] == '#':
            ans_tmp.append(0)
            q.append([j,i+1])
        elif tmp[j] == '×':
            ans_tmp.append(0)
        else:
            ans_tmp.append(10**4)
    c.append(tmp)
    ans.append(ans_tmp)

c.append(['×' for _ in range(W+2)])
ans.append([0 for _ in range(W+2)])


def bfs(q):
    while q:
        x,y = q.popleft()
        if c[y][x-1] == '.':
            q.append([x-1,y])
            ans[y][x-1] = ans[y][x] + 1
            c[y][x-1] = '#'
        if c[y][x+1] == '.':
            q.append([x+1,y])
            ans[y][x+1] = ans[y][x] + 1
            c[y][x+1] = '#'
        if c[y-1][x] == '.':
            q.append([x,y-1])
            ans[y-1][x] = ans[y][x] + 1
            c[y-1][x] = '#'
        if c[y+1][x] == '.':
            q.append([x,y+1])
            ans[y+1][x] = ans[y][x] + 1
            c[y+1][x] = '#'

bfs(q)
max_ans = 0
for i in range(H+2):
    #print(ans[i])
    max_ans = max(max_ans,max(ans[i]))

print(max_ans)
"""))