Buggy python submission (verdict: Runtime Error):
import sys,queue,math,copy,itertools,bisect,collections,heapq

def main():
    LI = lambda : [int(x) for x in sys.stdin.readline().split()]
    _LI = lambda : [int(x)-1 for x in sys.stdin.readline().split()]
    NI = lambda : int(sys.stdin.readline())
    SI = lambda : sys.stdin.readline().rstrip()

    H,W = LI()
    ch, cw = _LI()
    dh, dw = _LI()
    m = [[0] * W for _ in range(W)]
    for i in range(H):
        s = SI()
        for j in range(W):
            if s[j] == "#":
                m[i][j] = -1

    z = [(ch,cw,1)]
    while z:
        x,y,c = z.pop()
        if m[x][y]: continue
        q = collections.deque()
        q.append((x,y))
        m[x][y] = c
        r = [(x,y)]
        while q:
            x,y = q.popleft()
            if x == dh and y == dw:
                print(c-1)
                return
            for dx,dy in ((0,1),(1,0),(-1,0),(0,-1)):
                nx = x + dx
                ny = y + dy
                if not(0<= nx < H and 0<= ny < W): continue
                if m[nx][ny]: continue
                m[nx][ny] = c
                q.append((nx,ny))
                r.append((nx,ny))
        for x,y in r:
            for dx in range(-2,3):
                nx = x + dx
                if not(0<= nx < H): continue
                for dy in range(-2,3):
                    ny = y + dy
                    if not(0<= ny < W): continue
                    if m[nx][ny]: continue
                    z.append((nx,ny,c+1))
    print(-1)
if __name__ == '__main__':
    main()

Fixed submission:
import sys,queue,math,copy,itertools,bisect,collections,heapq

def main():
    LI = lambda : [int(x) for x in sys.stdin.readline().split()]
    _LI = lambda : [int(x)-1 for x in sys.stdin.readline().split()]
    NI = lambda : int(sys.stdin.readline())
    SI = lambda : sys.stdin.readline().rstrip()

    H,W = LI()
    ch, cw = _LI()
    dh, dw = _LI()
    m = [[0] * W for _ in range(H)]
    for i in range(H):
        s = SI()
        for j in range(W):
            if s[j] == "#":
                m[i][j] = -1

    z = collections.deque()
    z.append((ch,cw,1))
    while z:
        x,y,c = z.popleft()
        if m[x][y]: continue
        q = collections.deque()
        q.append((x,y))
        m[x][y] = c
        r = [(x,y)]
        while q:
            x,y = q.popleft()
            if x == dh and y == dw:
                print(c-1)
                return
            for dx,dy in ((0,1),(1,0),(-1,0),(0,-1)):
                nx = x + dx
                ny = y + dy
                if not(0<= nx < H and 0<= ny < W): continue
                if m[nx][ny]: continue
                m[nx][ny] = c
                q.append((nx,ny))
                r.append((nx,ny))
        for x,y in r:
            for dx in range(-2,3):
                nx = x + dx
                if not(0<= nx < H): continue
                for dy in range(-2,3):
                    ny = y + dy
                    if not(0<= ny < W): continue
                    if m[nx][ny]: continue
                    z.append((nx,ny,c+1))
    print(-1)
if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import sys,queue,math,copy,itertools,bisect,collections,heapq

def main():
    LI = lambda : [int(x) for x in sys.stdin.readline().split()]
    _LI = lambda : [int(x)-1 for x in sys.stdin.readline().split()]
    NI = lambda : int(sys.stdin.readline())
    SI = lambda : sys.stdin.readline().rstrip()

    H,W = LI()
    ch, cw = _LI()
    dh, dw = _LI()
    m = [[0] * W for _ in range(W)]
    for i in range(H):
        s = SI()
        for j in range(W):
            if s[j] == "#":
                m[i][j] = -1

    z = [(ch,cw,1)]
    while z:
        x,y,c = z.pop()
        q = collections.deque()
        q.append((x,y))
        m[x][y] = c
        r = [(x,y)]
        while q:
            x,y = q.popleft()
            if x == dh and y == dw:
                print(c-1)
                return
            for dx,dy in ((0,1),(1,0),(-1,0),(0,-1)):
                nx = x + dx
                ny = y + dy
                if not(0<= nx < H and 0<= ny < W): continue
                if m[nx][ny]: continue
                m[nx][ny] = c
                q.append((nx,ny))
                r.append((nx,ny))
        for x,y in r:
            for dx in range(-2,3):
                nx = x + dx
                if not(0<= nx < H): continue
                for dy in range(-2,3):
                    ny = y + dy
                    if not(0<= ny < W): continue
                    if m[nx][ny]: continue
                    z.append((nx,ny,c+1))
    print(-1)
if __name__ == '__main__':
    main()

Fixed submission:
import sys,queue,math,copy,itertools,bisect,collections,heapq

def main():
    LI = lambda : [int(x) for x in sys.stdin.readline().split()]
    _LI = lambda : [int(x)-1 for x in sys.stdin.readline().split()]
    NI = lambda : int(sys.stdin.readline())
    SI = lambda : sys.stdin.readline().rstrip()

    H,W = LI()
    ch, cw = _LI()
    dh, dw = _LI()
    m = [[0] * W for _ in range(H)]
    for i in range(H):
        s = SI()
        for j in range(W):
            if s[j] == "#":
                m[i][j] = -1

    z = collections.deque()
    z.append((ch,cw,1))
    while z:
        x,y,c = z.popleft()
        if m[x][y]: continue
        q = collections.deque()
        q.append((x,y))
        m[x][y] = c
        r = [(x,y)]
        while q:
            x,y = q.popleft()
            if x == dh and y == dw:
                print(c-1)
                return
            for dx,dy in ((0,1),(1,0),(-1,0),(0,-1)):
                nx = x + dx
                ny = y + dy
                if not(0<= nx < H and 0<= ny < W): continue
                if m[nx][ny]: continue
                m[nx][ny] = c
                q.append((nx,ny))
                r.append((nx,ny))
        for x,y in r:
            for dx in range(-2,3):
                nx = x + dx
                if not(0<= nx < H): continue
                for dy in range(-2,3):
                    ny = y + dy
                    if not(0<= ny < W): continue
                    if m[nx][ny]: continue
                    z.append((nx,ny,c+1))
    print(-1)
if __name__ == '__main__':
    main()