Buggy python submission (verdict: Time Limit Exceeded):
####################################################################
import sys
def _p(*_a):
  #return
  _s=" ".join(map(str,_a))
  #print(_s)
  sys.stderr.write(_s+"\n")
####################################################################
def _pa(_aa):
  #return
  for _a in _aa: _p(_a)
####################################################################
H,W = map(int, input().split())
ch,cw = map(int, input().split())
dh,dw = map(int, input().split())
M = list( list(input()) for _ in range(H) )

INF = 10**18

for h in range(H):
  for w in range(W):
    if M[h][w] == ".": M[h][w] = INF
    # if M[h][w] == "#": M[h][w] = -1

ch -= 1
cw -= 1
dh -= 1
dw -= 1

M[ch][cw] = 0
# M[dh][dw] = "G"

# _pa(M)


from collections import deque
Q = deque()
Q.append((ch,cw))

ans = INF

while Q:
  h,w = Q.popleft()

  for ih,iw in [(1,0), (-1,0), (0,1), (0,-1)]:
    nh = h + ih
    nw = w + iw
    if nh < 0 or H <= nh: continue
    if nw < 0 or W <= nw: continue
    if M[nh][nw] == "#": continue

    if nh == dh and nw == dw:
      M[nh][nw] = min(M[h][w], M[dh][dw])
      ans = min(ans, M[nh][nw])
      continue

    if M[h][w] < M[nh][nw]:
      M[nh][nw] = M[h][w]
      Q.append((nh,nw))
      continue

    if M[h][w] > M[nh][nw]:
      M[h][w] = M[nh][nw]
      Q.append((h,w))

  for ih,iw in [(1,1), (1,-1), (-1,1), (-1,-1), (2,0), (2,1), (2,2), (2,-1), (2,-2), (1,2), (1,-2), (0,2), (0,-2), (-1,2), (-1,-2), (-2,0), (-2,1), (-2,-2), (-2,-1), (-2,-2)]:
    nh = h + ih
    nw = w + iw
    if nh < 0 or H <= nh: continue
    if nw < 0 or W <= nw: continue
    if M[nh][nw] == "#": continue

    if nh == dh and nw == dw:
      M[nh][nw] = min(M[h][w]+1, M[dh][dw])
      ans = min(ans, M[nh][nw])
      continue

    if M[h][w]+1 < M[nh][nw]:
      M[nh][nw] = M[h][w]+1
      Q.append((nh,nw))
      continue

    if M[h][w] > M[nh][nw]+1:
      M[h][w] = M[nh][nw]+1
      Q.append((h,w))

# _pa(M)

if ans == INF: ans = -1
print(ans)


















Fixed submission:
####################################################################
import sys
def _p(*_a):
  #return
  _s=" ".join(map(str,_a))
  #print(_s)
  sys.stderr.write(_s+"\n")
####################################################################
def _pa(_aa):
  #return
  for _a in _aa: _p(_a)
####################################################################
H,W = map(int, input().split())
ch,cw = map(int, input().split())
dh,dw = map(int, input().split())
M = list( list(input()) for _ in range(H) )

if ch==dh and cw==dw:
  print(0)
  exit()

INF = 10**18

for h in range(H):
  for w in range(W):
    if M[h][w] == ".": M[h][w] = INF
    # if M[h][w] == "#": M[h][w] = -1

ch -= 1
cw -= 1
dh -= 1
dw -= 1

M[ch][cw] = 0
# M[dh][dw] = "G"

# _pa(M)


from collections import deque
Q = deque()
Q.append((ch,cw))

ans = INF

while Q:
  h,w = Q.popleft()

  for ih,iw in [(1,0), (-1,0), (0,1), (0,-1)]:
    nh = h + ih
    nw = w + iw
    if nh < 0 or H <= nh: continue
    if nw < 0 or W <= nw: continue
    if M[nh][nw] == "#": continue

    if nh == dh and nw == dw:
      M[nh][nw] = min(M[h][w], M[dh][dw])
      ans = min(ans, M[nh][nw])
      continue

    if M[h][w] < M[nh][nw]:
      M[nh][nw] = M[h][w]
      Q.appendleft((nh,nw))
      continue

    if M[h][w] > M[nh][nw]:
      M[h][w] = M[nh][nw]
      Q.appendleft((h,w))

  for ih,iw in [(1,1), (1,-1), (-1,1), (-1,-1), (2,0), (2,1), (2,2), (2,-1), (2,-2), (1,2), (1,-2), (0,2), (0,-2), (-1,2), (-1,-2), (-2,0), (-2,1), (-2,-2), (-2,-1), (-2,-2)]:
    nh = h + ih
    nw = w + iw
    if nh < 0 or H <= nh: continue
    if nw < 0 or W <= nw: continue
    if M[nh][nw] == "#": continue

    if nh == dh and nw == dw:
      M[nh][nw] = min(M[h][w]+1, M[dh][dw])
      ans = min(ans, M[nh][nw])
      continue

    if M[h][w]+1 < M[nh][nw]:
      M[nh][nw] = M[h][w]+1
      Q.append((nh,nw))
      continue

    if M[h][w] > M[nh][nw]+1:
      M[h][w] = M[nh][nw]+1
      Q.append((h,w))

# _pa(M)

if ans == INF: ans = -1
print(ans)