Buggy python submission (verdict: Runtime Error):
class Grid:
    def __init__(self, H, W, grid, road_wall=(".", "#")):
        self.road, self.wall = road_wall
        self.H = H
        self.W = W
        self.grid = grid
        self.parent = [[-1] * self.W for _ in range(self.H)]
        self.move = [(1, 0), (-1, 0), (0, 1), (0, -1)]     # 動ける場所の候補
        self.move2 = dict()
        self.move2[(1,0)] = [(2,-1),(2,0),(2,1),(2,2),(1,1)]
        self.move2[(-1,0)] = [(-2,-1),(-2,0),(-2,1),(-2,-2),(-1,-1)]
        self.move2[(0,1)] = [(1,2),(0,2),(-1,2),(-2,2),(-1,1)]
        self.move2[(0,-1)] = [(1,-2),(0,-2),(-1,-2),(2,-2),(1,-1)]

    def bfs(self, start=(0,0), goal=-3, time=0, save=False):
        """
        :param start: スタート地点
        :param goal: ゴール地点
        :param save: True = 前回の探索結果を保持する
        :return: （ループがあっても）最短距離。存在しなければ -1
        """
        if save:
            parent = self.parent
        else:
            parent = [[-1] * self.W for _ in range(self.H)]
        p, t = start, time
        parent[p[0]][p[1]] = -2
        next_set = [[(p, t)]]
        broken_set = [[]]
        while next_set:
            while next_set:
                p, t = next_set.pop()
                h, w = p
                for dh, dw in self.move:
                    q = (h + dh, w + dw)
                    if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                        continue
                    if parent[q[0]][q[1]] != -1:
                        continue
                    if self.grid[q[0]][q[1]] == self.wall:         # 壁があったら進まない
                        for dh2, dw2 in self.move2[(dh,dw)]:
                            r = (h + dh2, w + dw2)
                            broken_set.append((r, t))
                        continue
                    if q == goal:
                        return t
                    #### (debug code) ######
                    # self.debug(start, goal, q, t)
                    ########################
                    parent[q[0]][q[1]] = p
                    next_set.append((q, t))
            while broken_set:
                q, t = broken_set.pop()
                if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                    continue
                if parent[q[0]][q[1]] != -1:
                    continue
                if self.grid[q[0]][q[1]] == self.wall:  # 壁があったら進まない
                    continue
                if q == goal:
                    return t + 1
                parent[q[0]][q[1]] = 1
                next_set.append((q, t+1))
        return -1

    def debug(self, start, goal, p, t):
        player = p
        debug_grid = list(list(self.grid[h]) for h in range(self.H))
        if start != (None, None):
            debug_grid[start[0]][start[1]] = "S"
        if goal != -3:
            debug_grid[goal[0]][goal[1]] = "G"
        debug_grid[player[0]][player[1]] = "P"
        print("~~~~~~~~~ t = " + str(t + 1) + "  ~~~~~~~~")
        for debug_h in range(self.H):
            print("".join(str(debug_grid[debug_h][debug_w]) for debug_w in range(self.W)))


############################################################################################

import sys
input = sys.stdin.readline



road, wall = ".", "#"                         # (進行可能を意味する記号, 進行不可を意味する記号)

H, W = map(int,input().split())                # 左上は(h,w)=(0,0)、右下は(h,w)=(H-1,W-1)
x, y = map(int, input().split())
start = (x-1,y-1)
x, y = map(int, input().split())
goal = (x-1,y-1)
grid = []
for h in range(H):
    grid.append(input().rstrip())

g = Grid(H, W, grid, (road, wall))
res = g.bfs(start=start, goal=goal)
print(res)


Fixed submission:
class Grid:
    def __init__(self, H, W, grid, road_wall=(".", "#")):
        self.road, self.wall = road_wall
        self.H = H
        self.W = W
        self.grid = grid
        self.parent = [[-1] * self.W for _ in range(self.H)]
        self.move = [(1, 0), (-1, 0), (0, 1), (0, -1)]     # 動ける場所の候補
        self.move2 = dict()
        self.move2 = [(-2, 0), (2, 1), (1, -2), (1, -1), (1, 2), (-2, 1), (-1, 1), (-2, -1), (-2, -2), (-1, -1), (-1, -2), (2, 2), (1, 1), (2, -1), (-1, 2), (-2, 2), (2, -2), (2, 0), (0, -2), (0, 2)]

    def bfs(self, start=(0,0), goal=-3, time=0, save=False):
        """
        :param start: スタート地点
        :param goal: ゴール地点
        :param save: True = 前回の探索結果を保持する
        :return: （ループがあっても）最短距離。存在しなければ -1
        """
        if save:
            parent = self.parent
        else:
            parent = [[-1] * self.W for _ in range(self.H)]
        p, t = start, time
        parent[p[0]][p[1]] = -2
        next_set = deque([(p, t)])
        broken_set = deque([])
        while next_set:
            while next_set:
                p, t = next_set.popleft()
                h, w = p
                for dh, dw in self.move:
                    q = (h + dh, w + dw)
                    if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                        continue
                    if parent[q[0]][q[1]] != -1:
                        continue
                    if q == goal:
                        return t
                    parent[q[0]][q[1]] = p
                    if self.grid[q[0]][q[1]] == self.wall:         # 壁があったら進まない
                        for dh2, dw2 in self.move2:
                            r = (h + dh2, w + dw2)
                            broken_set.append((r, t))
                        continue
                    #### (debug code) ######
                    # self.debug(start, goal, q, t)
                    ########################
                    next_set.append((q, t))
            while broken_set:
                q, t = broken_set.popleft()
                if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                    continue
                if parent[q[0]][q[1]] != -1:
                    continue
                if self.grid[q[0]][q[1]] == self.wall:  # 壁があったら進まない
                    continue
                if q == goal:
                    return t + 1
                #### (debug code) ######
                # self.debug(start, goal, q, t)
                ########################
                next_set.append((q, t+1))
        return -1

    def debug(self, start, goal, p, t):
        player = p
        debug_grid = list(list(self.grid[h]) for h in range(self.H))
        if start != (None, None):
            debug_grid[start[0]][start[1]] = "S"
        if goal != -3:
            debug_grid[goal[0]][goal[1]] = "G"
        debug_grid[player[0]][player[1]] = "P"
        print("~~~~~~~~~ t = " + str(t + 1) + "  ~~~~~~~~")
        for debug_h in range(self.H):
            print("".join(str(debug_grid[debug_h][debug_w]) for debug_w in range(self.W)))


############################################################################################

from collections import deque
import sys
input = sys.stdin.readline

road, wall = ".", "#"                         # (進行可能を意味する記号, 進行不可を意味する記号)

H, W = map(int,input().split())                # 左上は(h,w)=(0,0)、右下は(h,w)=(H-1,W-1)
x, y = map(int, input().split())
start = (x-1,y-1)
x, y = map(int, input().split())
goal = (x-1,y-1)
grid = []
for h in range(H):
    grid.append(input().rstrip())

g = Grid(H, W, grid, (road, wall))
res = g.bfs(start=start, goal=goal)
print(res)

"""
5 6
5 6
1 1
.###.#
######
#..##.
######
#####.
"""

Buggy python submission (verdict: Time Limit Exceeded):
class Grid:
    def __init__(self, H, W, grid, road_wall=(".", "#")):
        self.road, self.wall = road_wall
        self.H = H
        self.W = W
        self.grid = grid
        self.parent = [[-1] * self.W for _ in range(self.H)]
        self.move = [(1, 0), (-1, 0), (0, 1), (0, -1)]     # 動ける場所の候補
        self.move2 = dict()
        self.move2[(1,0)] = [(2,-1),(2,0),(2,1),(2,2)]
        self.move2[(-1,0)] = [(-2,-1),(-2,0),(-2,1),(-2,-2)]
        self.move2[(0,1)] = [(1,2),(0,2),(-1,2),(-2,2)]
        self.move2[(0,-1)] = [(1,-2),(0,-2),(-1,-2),(2,-2)]

    def bfs(self, start=(0,0), goal=-3, time=0, save=False):
        """
        :param start: スタート地点
        :param goal: ゴール地点
        :param save: True = 前回の探索結果を保持する
        :return: （ループがあっても）最短距離。存在しなければ -1
        """
        if save:
            parent = self.parent
        else:
            parent = [[-1] * self.W for _ in range(self.H)]
        p, t = start, time
        parent[p[0]][p[1]] = -2
        next_set = deque([(p, t)])
        broken_set = deque([])
        while next_set:
            while next_set:
                p, t = next_set.popleft()
                h, w = p
                for dh, dw in self.move:
                    q = (h + dh, w + dw)
                    if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                        continue
                    if parent[q[0]][q[1]] != -1:
                        continue
                    if self.grid[q[0]][q[1]] == self.wall:         # 壁があったら進まない
                        for dh2, dw2 in self.move2[(dh,dw)]:
                            r = (h + dh2, w + dw2)
                            broken_set.append((r, t))
                        continue
                    if q == goal:
                        return t
                    #### (debug code) ######
                    # self.debug(start, goal, q, t)
                    ########################
                    parent[q[0]][q[1]] = p
                    next_set.append((q, t))
            while broken_set != deque([]):
                q, t = broken_set.popleft()
                if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                    continue
                if parent[q[0]][q[1]] != -1:
                    continue
                if self.grid[q[0]][q[1]] == self.wall:  # 壁があったら進まない
                    continue
                if q == goal:
                    return t + 1
                next_set.append((q, t+1))
        return -1

    def debug(self, start, goal, p, t):
        player = p
        debug_grid = list(list(self.grid[h]) for h in range(self.H))
        if start != (None, None):
            debug_grid[start[0]][start[1]] = "S"
        if goal != -3:
            debug_grid[goal[0]][goal[1]] = "G"
        debug_grid[player[0]][player[1]] = "P"
        print("~~~~~~~~~ t = " + str(t + 1) + "  ~~~~~~~~")
        for debug_h in range(self.H):
            print("".join(str(debug_grid[debug_h][debug_w]) for debug_w in range(self.W)))


############################################################################################

from collections import deque
import sys
input = sys.stdin.readline



road, wall = ".", "#"                         # (進行可能を意味する記号, 進行不可を意味する記号)

H, W = map(int,input().split())                # 左上は(h,w)=(0,0)、右下は(h,w)=(H-1,W-1)
x, y = map(int, input().split())
start = (x-1,y-1)
x, y = map(int, input().split())
goal = (x-1,y-1)
grid = []
for h in range(H):
    grid.append(input().rstrip())

g = Grid(H, W, grid, (road, wall))
res = g.bfs(start=start, goal=goal)
print(res)

Fixed submission:
class Grid:
    def __init__(self, H, W, grid, road_wall=(".", "#")):
        self.road, self.wall = road_wall
        self.H = H
        self.W = W
        self.grid = grid
        self.parent = [[-1] * self.W for _ in range(self.H)]
        self.move = [(1, 0), (-1, 0), (0, 1), (0, -1)]     # 動ける場所の候補
        self.move2 = dict()
        self.move2 = [(-2, 0), (2, 1), (1, -2), (1, -1), (1, 2), (-2, 1), (-1, 1), (-2, -1), (-2, -2), (-1, -1), (-1, -2), (2, 2), (1, 1), (2, -1), (-1, 2), (-2, 2), (2, -2), (2, 0), (0, -2), (0, 2)]

    def bfs(self, start=(0,0), goal=-3, time=0, save=False):
        """
        :param start: スタート地点
        :param goal: ゴール地点
        :param save: True = 前回の探索結果を保持する
        :return: （ループがあっても）最短距離。存在しなければ -1
        """
        if save:
            parent = self.parent
        else:
            parent = [[-1] * self.W for _ in range(self.H)]
        p, t = start, time
        parent[p[0]][p[1]] = -2
        next_set = deque([(p, t)])
        broken_set = deque([])
        while next_set:
            while next_set:
                p, t = next_set.popleft()
                h, w = p
                for dh, dw in self.move:
                    q = (h + dh, w + dw)
                    if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                        continue
                    if parent[q[0]][q[1]] != -1:
                        continue
                    if q == goal:
                        return t
                    parent[q[0]][q[1]] = p
                    if self.grid[q[0]][q[1]] == self.wall:         # 壁があったら進まない
                        for dh2, dw2 in self.move2:
                            r = (h + dh2, w + dw2)
                            broken_set.append((r, t))
                        continue
                    #### (debug code) ######
                    # self.debug(start, goal, q, t)
                    ########################
                    next_set.append((q, t))
            while broken_set:
                q, t = broken_set.popleft()
                if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                    continue
                if parent[q[0]][q[1]] != -1:
                    continue
                if self.grid[q[0]][q[1]] == self.wall:  # 壁があったら進まない
                    continue
                if q == goal:
                    return t + 1
                #### (debug code) ######
                # self.debug(start, goal, q, t)
                ########################
                next_set.append((q, t+1))
        return -1

    def debug(self, start, goal, p, t):
        player = p
        debug_grid = list(list(self.grid[h]) for h in range(self.H))
        if start != (None, None):
            debug_grid[start[0]][start[1]] = "S"
        if goal != -3:
            debug_grid[goal[0]][goal[1]] = "G"
        debug_grid[player[0]][player[1]] = "P"
        print("~~~~~~~~~ t = " + str(t + 1) + "  ~~~~~~~~")
        for debug_h in range(self.H):
            print("".join(str(debug_grid[debug_h][debug_w]) for debug_w in range(self.W)))


############################################################################################

from collections import deque
import sys
input = sys.stdin.readline

road, wall = ".", "#"                         # (進行可能を意味する記号, 進行不可を意味する記号)

H, W = map(int,input().split())                # 左上は(h,w)=(0,0)、右下は(h,w)=(H-1,W-1)
x, y = map(int, input().split())
start = (x-1,y-1)
x, y = map(int, input().split())
goal = (x-1,y-1)
grid = []
for h in range(H):
    grid.append(input().rstrip())

g = Grid(H, W, grid, (road, wall))
res = g.bfs(start=start, goal=goal)
print(res)

"""
5 6
5 6
1 1
.###.#
######
#..##.
######
#####.
"""

Buggy python submission (verdict: Time Limit Exceeded):
class Grid:
    def __init__(self, H, W, grid, road_wall=(".", "#")):
        self.road, self.wall = road_wall
        self.H = H
        self.W = W
        self.grid = grid
        self.parent = [[-1] * self.W for _ in range(self.H)]
        self.move = [(1, 0), (-1, 0), (0, 1), (0, -1)]     # 動ける場所の候補
        self.move2 = [(2,0),(2,1),(2,2),(1,2),(0,2),(-1,2),(-2,2),(-2,1),(-2,0),(-2,-1),(-2,-2),(-1,-2),(0,-2),(1,-2),(2,-2),(2,-1)]

    def bfs(self, start=(0,0), goal=-3, time=0, save=False):
        """
        :param start: スタート地点
        :param goal: ゴール地点
        :param save: True = 前回の探索結果を保持する
        :return: （ループがあっても）最短距離。存在しなければ -1
        """
        if save:
            parent = self.parent
        else:
            parent = [[-1] * self.W for _ in range(self.H)]
        p, t = start, time
        parent[p[0]][p[1]] = -2
        next_set = deque([(p, t)])
        broken_set = deque([])
        while next_set:
            while next_set:
                p, t = next_set.popleft()
                h, w = p
                for dh, dw in self.move:
                    q = (h + dh, w + dw)
                    if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                        continue
                    if parent[q[0]][q[1]] != -1:
                        continue
                    if self.grid[q[0]][q[1]] == self.wall:         # 壁があったら進まない
                        for dh, dw in self.move2:
                            r = (h + dh, w + dw)
                            broken_set.append((r, t))
                        continue
                    if q == goal:
                        return t
                    #### (debug code) ######
                    # self.debug(start, goal, q, t)
                    ########################
                    parent[q[0]][q[1]] = p
                    next_set.append((q, t))
            while broken_set != deque([]):
                q, t = broken_set.popleft()
                if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                    continue
                if parent[q[0]][q[1]] != -1:
                    continue
                if self.grid[q[0]][q[1]] == self.wall:  # 壁があったら進まない
                    continue
                if q == goal:
                    return t + 1
                next_set.append((q, t+1))
        return -1

    def debug(self, start, goal, p, t):
        player = p
        debug_grid = list(list(self.grid[h]) for h in range(self.H))
        if start != (None, None):
            debug_grid[start[0]][start[1]] = "S"
        if goal != -3:
            debug_grid[goal[0]][goal[1]] = "G"
        debug_grid[player[0]][player[1]] = "P"
        print("~~~~~~~~~ t = " + str(t + 1) + "  ~~~~~~~~")
        for debug_h in range(self.H):
            print("".join(str(debug_grid[debug_h][debug_w]) for debug_w in range(self.W)))


############################################################################################

from collections import deque
import sys
input = sys.stdin.readline



road, wall = ".", "#"                         # (進行可能を意味する記号, 進行不可を意味する記号)

H, W = map(int,input().split())                # 左上は(h,w)=(0,0)、右下は(h,w)=(H-1,W-1)
x, y = map(int, input().split())
start = (x-1,y-1)
x, y = map(int, input().split())
goal = (x-1,y-1)
grid = []
for h in range(H):
    grid.append(input().rstrip())

g = Grid(H, W, grid, (road, wall))
res = g.bfs(start=start, goal=goal)
print(res)

Fixed submission:
class Grid:
    def __init__(self, H, W, grid, road_wall=(".", "#")):
        self.road, self.wall = road_wall
        self.H = H
        self.W = W
        self.grid = grid
        self.parent = [[-1] * self.W for _ in range(self.H)]
        self.move = [(1, 0), (-1, 0), (0, 1), (0, -1)]     # 動ける場所の候補
        self.move2 = dict()
        self.move2 = [(-2, 0), (2, 1), (1, -2), (1, -1), (1, 2), (-2, 1), (-1, 1), (-2, -1), (-2, -2), (-1, -1), (-1, -2), (2, 2), (1, 1), (2, -1), (-1, 2), (-2, 2), (2, -2), (2, 0), (0, -2), (0, 2)]

    def bfs(self, start=(0,0), goal=-3, time=0, save=False):
        """
        :param start: スタート地点
        :param goal: ゴール地点
        :param save: True = 前回の探索結果を保持する
        :return: （ループがあっても）最短距離。存在しなければ -1
        """
        if save:
            parent = self.parent
        else:
            parent = [[-1] * self.W for _ in range(self.H)]
        p, t = start, time
        parent[p[0]][p[1]] = -2
        next_set = deque([(p, t)])
        broken_set = deque([])
        while next_set:
            while next_set:
                p, t = next_set.popleft()
                h, w = p
                for dh, dw in self.move:
                    q = (h + dh, w + dw)
                    if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                        continue
                    if parent[q[0]][q[1]] != -1:
                        continue
                    if q == goal:
                        return t
                    parent[q[0]][q[1]] = p
                    if self.grid[q[0]][q[1]] == self.wall:         # 壁があったら進まない
                        for dh2, dw2 in self.move2:
                            r = (h + dh2, w + dw2)
                            broken_set.append((r, t))
                        continue
                    #### (debug code) ######
                    # self.debug(start, goal, q, t)
                    ########################
                    next_set.append((q, t))
            while broken_set:
                q, t = broken_set.popleft()
                if q[0] < 0 or q[0] >= self.H or q[1] < 0 or q[1] >= self.W:
                    continue
                if parent[q[0]][q[1]] != -1:
                    continue
                if self.grid[q[0]][q[1]] == self.wall:  # 壁があったら進まない
                    continue
                if q == goal:
                    return t + 1
                #### (debug code) ######
                # self.debug(start, goal, q, t)
                ########################
                next_set.append((q, t+1))
        return -1

    def debug(self, start, goal, p, t):
        player = p
        debug_grid = list(list(self.grid[h]) for h in range(self.H))
        if start != (None, None):
            debug_grid[start[0]][start[1]] = "S"
        if goal != -3:
            debug_grid[goal[0]][goal[1]] = "G"
        debug_grid[player[0]][player[1]] = "P"
        print("~~~~~~~~~ t = " + str(t + 1) + "  ~~~~~~~~")
        for debug_h in range(self.H):
            print("".join(str(debug_grid[debug_h][debug_w]) for debug_w in range(self.W)))


############################################################################################

from collections import deque
import sys
input = sys.stdin.readline

road, wall = ".", "#"                         # (進行可能を意味する記号, 進行不可を意味する記号)

H, W = map(int,input().split())                # 左上は(h,w)=(0,0)、右下は(h,w)=(H-1,W-1)
x, y = map(int, input().split())
start = (x-1,y-1)
x, y = map(int, input().split())
goal = (x-1,y-1)
grid = []
for h in range(H):
    grid.append(input().rstrip())

g = Grid(H, W, grid, (road, wall))
res = g.bfs(start=start, goal=goal)
print(res)

"""
5 6
5 6
1 1
.###.#
######
#..##.
######
#####.
"""