Buggy python submission (verdict: Time Limit Exceeded):
h,w = map(int,input().split())
n = h * w
raw = []
for i in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(1)
  raw += add
wf = [[100 for _ in range(n)] for _ in range(n)]
for i in range(n):
  if raw[i] == 0:
    wf[i][i] = 0
    d = []
    if i-w >= 0:
      d.append(i-w)
    if i+w < n:
      d.append(i+w)
    if i%w != 0:
      d.append(i-1)
    if (i+1)%w != 0:
      d.append(i+1)
    for e in d:
      try:
        if raw[e] == 0:
          wf[i][e] = 1
      except:
        print(e)
#for x in wf:
  #print(x)
for k in range(n):
  for i in range(n):
    for j in range(n):
      if wf[i][k] + wf[k][j] < wf[i][j]:
        wf[i][j] = wf[i][k] + wf[k][j]
ans = 0
for i in range(n):
  for j in range(n):
    if ans < wf[i][j] % 100:
      ans = wf[i][j]
print(ans)
#for x in wf:
  #print(x)

Fixed submission:
h,w = map(int,input().split())
n = h * w
raw = []
for i in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(1)
  raw += add
wf = [[1000 for _ in range(n)] for _ in range(n)]
for i in range(n):
  if raw[i] == 0:
    wf[i][i] = 0
    d = []
    if i-w >= 0:
      d.append(i-w)
    if i+w < n:
      d.append(i+w)
    if i%w != 0:
      d.append(i-1)
    if (i+1)%w != 0:
      d.append(i+1)
    for e in d:
      if raw[e] == 0:
        wf[i][e] = 1
#for x in wf:
  #print(x)
for k in range(n):
  for i in range(n):
    for j in range(n):
      if wf[i][k] + wf[k][j] < wf[i][j]:
        wf[i][j] = wf[i][k] + wf[k][j]
ans = 0
for i in range(n):
  for j in range(n):
    if ans < wf[i][j] % 1000:
      ans = wf[i][j]
print(ans)
#for x in wf:
  #print(x)

Buggy python submission (verdict: Time Limit Exceeded):
h,w = map(int,input().split())
raw = []
for _ in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(2)
  raw.append(add)
nex = [[0,1],[0,-1],[1,0],[-1,0]]
can = []
from copy import deepcopy as dc
for a in range(h):
  for b in range(w):
    if raw[a][b] == 2:
      continue
    now = dc(raw)
    now[a][b] = 1
    ans = 0
    while True:
      last = dc(now)
      ans += 1
      check = 1
      for i in range(h):
        for j in range(w):
          if last[i][j] == 0:
            for x in nex:
              if 0 <= i+x[0] < h and 0 <= j+x[1] < w:
                if last[i+x[0]][j+x[1]] == 1:
                  now[i][j] = 1
                  break
            else:
              check = 0
      if check == 1:
        can.append(ans)
        break
print(max(can))

Fixed submission:
h,w = map(int,input().split())
n = h * w
raw = []
for i in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(1)
  raw += add
wf = [[1000 for _ in range(n)] for _ in range(n)]
for i in range(n):
  if raw[i] == 0:
    wf[i][i] = 0
    d = []
    if i-w >= 0:
      d.append(i-w)
    if i+w < n:
      d.append(i+w)
    if i%w != 0:
      d.append(i-1)
    if (i+1)%w != 0:
      d.append(i+1)
    for e in d:
      if raw[e] == 0:
        wf[i][e] = 1
#for x in wf:
  #print(x)
for k in range(n):
  for i in range(n):
    for j in range(n):
      if wf[i][k] + wf[k][j] < wf[i][j]:
        wf[i][j] = wf[i][k] + wf[k][j]
ans = 0
for i in range(n):
  for j in range(n):
    if ans < wf[i][j] % 1000:
      ans = wf[i][j]
print(ans)
#for x in wf:
  #print(x)

Buggy python submission (verdict: Time Limit Exceeded):
h,w = map(int,input().split())
raw = []
for _ in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(2)
  raw.append(add)
nex = [[0,1],[0,-1],[1,0],[-1,0]]
can = []
from copy import deepcopy as dc
for a in range(h):
  for b in range(w):
    if raw[a][b] == 2:
      continue
    now = dc(raw)
    now[a][b] = 1
    ans = 0
    while True:
      last = dc(now)
      ans += 1
      check = 1
      for i in range(h):
        for j in range(w):
          if last[i][j] == 0:
            for x in nex:
              if 0 <= i+x[0] < h and 0 <= j+x[1] < w:
                if last[i+x[0]][j+x[1]] == 1:
                  now[i][j] = 1
                  break
            else:
              check = 0
      if check == 1:
        can.append(ans)
        break
print(max(can))

Fixed submission:
h,w = map(int,input().split())
n = h * w
raw = []
for i in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(1)
  raw += add
wf = [[1000 for _ in range(n)] for _ in range(n)]
for i in range(n):
  if raw[i] == 0:
    wf[i][i] = 0
    d = []
    if i-w >= 0:
      d.append(i-w)
    if i+w < n:
      d.append(i+w)
    if i%w != 0:
      d.append(i-1)
    if (i+1)%w != 0:
      d.append(i+1)
    for e in d:
      if raw[e] == 0:
        wf[i][e] = 1
#for x in wf:
  #print(x)
for k in range(n):
  for i in range(n):
    for j in range(n):
      if wf[i][k] + wf[k][j] < wf[i][j]:
        wf[i][j] = wf[i][k] + wf[k][j]
ans = 0
for i in range(n):
  for j in range(n):
    if ans < wf[i][j] % 1000:
      ans = wf[i][j]
print(ans)
#for x in wf:
  #print(x)

Buggy python submission (verdict: Time Limit Exceeded):
h,w = map(int,input().split())
raw = []
for _ in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(2)
  raw.append(add)
nex = [[0,1],[0,-1],[1,0],[-1,0]]
can = []
from copy import deepcopy as dc
for a in range(h):
  for b in range(w):
    if raw[a][b] == 2:
      continue
    last = dc(raw)
    last[a][b] = 1
    ans = 0
    while True:
      now = dc(last)
      ans += 1
      for i in range(h):
        for j in range(w):
          if last[i][j] == 0:
            for x in nex:
              if 0 <= i+x[0] < h and 0 <= j+x[1] < w:
                if last[i+x[0]][j+x[1]] == 1:
                  now[i][j] = 1
                  break
      check = 1
      for i in range(h):
        for j in range(w):
          check *= now[i][j]
      if check > 0:
        can.append(ans)
        break
      last = dc(now)
print(max(can))

Fixed submission:
h,w = map(int,input().split())
n = h * w
raw = []
for i in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(1)
  raw += add
wf = [[1000 for _ in range(n)] for _ in range(n)]
for i in range(n):
  if raw[i] == 0:
    wf[i][i] = 0
    d = []
    if i-w >= 0:
      d.append(i-w)
    if i+w < n:
      d.append(i+w)
    if i%w != 0:
      d.append(i-1)
    if (i+1)%w != 0:
      d.append(i+1)
    for e in d:
      if raw[e] == 0:
        wf[i][e] = 1
#for x in wf:
  #print(x)
for k in range(n):
  for i in range(n):
    for j in range(n):
      if wf[i][k] + wf[k][j] < wf[i][j]:
        wf[i][j] = wf[i][k] + wf[k][j]
ans = 0
for i in range(n):
  for j in range(n):
    if ans < wf[i][j] % 1000:
      ans = wf[i][j]
print(ans)
#for x in wf:
  #print(x)

Buggy python submission (verdict: Time Limit Exceeded):
h,w = map(int,input().split())
raw = []
for _ in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(2)
  raw.append(add)
nex = [[0,1],[0,-1],[1,0],[-1,0]]
can = []
from copy import deepcopy as dc
for a in range(h):
  for b in range(w):
    if raw[a][b] == 2:
      continue
    last = dc(raw)
    last[a][b] = 1
    ans = 0
    while True:
      now = dc(last)
      ans += 1
      for i in range(h):
        for j in range(w):
          if last[i][j] == 1:
            for x in nex:
              if 0 <= i+x[0] < h and 0 <= j+x[1] < w:
                if now[i+x[0]][j+x[1]] == 0:
                  now[i+x[0]][j+x[1]] = 1
      check = 1
      for i in range(h):
        for j in range(w):
          check *= now[i][j]
      if check > 0:
        can.append(ans)
        #print(a,b)
        #for y in now:
          #print(y)
        break
      #if (a,b) == (0,4):
        #print(ans)
        #for y in now:
          #print(y)
      last = dc(now)
print(max(can))
#print(can)
#print(raw)

Fixed submission:
h,w = map(int,input().split())
n = h * w
raw = []
for i in range(h):
  tmp = input()
  add = []
  for j in range(w):
    if tmp[j] == '.':
      add.append(0)
    else:
      add.append(1)
  raw += add
wf = [[1000 for _ in range(n)] for _ in range(n)]
for i in range(n):
  if raw[i] == 0:
    wf[i][i] = 0
    d = []
    if i-w >= 0:
      d.append(i-w)
    if i+w < n:
      d.append(i+w)
    if i%w != 0:
      d.append(i-1)
    if (i+1)%w != 0:
      d.append(i+1)
    for e in d:
      if raw[e] == 0:
        wf[i][e] = 1
#for x in wf:
  #print(x)
for k in range(n):
  for i in range(n):
    for j in range(n):
      if wf[i][k] + wf[k][j] < wf[i][j]:
        wf[i][j] = wf[i][k] + wf[k][j]
ans = 0
for i in range(n):
  for j in range(n):
    if ans < wf[i][j] % 1000:
      ans = wf[i][j]
print(ans)
#for x in wf:
  #print(x)