Buggy python submission (verdict: Runtime Error):
f = open("C:/Users/naoki/Desktop/Atcoder/input.txt")

H, W = map(int, f.readline().split())
C = list(map(lambda x: int(x)-1, f.readline().split()))
D = list(map(lambda x: int(x)-1, f.readline().split()))

Ss = [str(f.readline()) for _ in range(H)]
group = [[-1 for _ in range(W)] for _ in range(H)]

moves = [[-1,0], [1,0], [0,-1], [0,1]]

from collections import deque
todo = deque()
now_group = -1
for i in range(H):
    for j in range(W):
        if group[i][j] == -1 and Ss[i][j]==".":
            todo.append([i,j])
            now_group += 1
            group[i][j] = now_group
        while len(todo) > 0:
            checking = todo.pop()
            for move in moves:
                now = [checking[0]+move[0],checking[1]+move[1]]
                if not (0 <= now[0] <H and 0 <= now[1] <W):
                    continue
                if group[now[0]][now[1]] == -1 and Ss[now[0]][now[1]]==".":
                    todo.append(now)
                    group[now[0]][now[1]] = now_group

can_waap = [set() for _ in range(now_group+1)]

for i in range(H):
    for j in range(W):
        if group[i][j] ==-1:
            continue
        for yoko in range(-2,3):
            for tate in range(-2,3):
                now = [tate+i, yoko+j]
                if not (0<=now[0]<H and 0<=now[1]<W):
                    continue
                if group[now[0]][now[1]] == -1:
                    continue
                
                if group[i][j] != group[now[0]][now[1]]:
                    can_waap[group[i][j]].add(group[now[0]][now[1]])
                    can_waap[group[now[0]][now[1]]].add(group[i][j])
start = group[C[0]][C[1]]
goal = group[D[0]][D[1]]
import sys
import copy
seen = set([start])
nows = [start]

if start==goal:
    print(0)
    sys.exit()

for step in range(now_group+1):
    pre_nows = copy.deepcopy(nows)
    nows = []
    for pre_now in range(len(pre_nows)):
        for j in can_waap[pre_now]:
            if j not in seen:
                seen.add(j)
                nows.append(j)
                if j == goal:
                    print(step+1)
                    sys.exit()

print(-1)

Fixed submission:
H, W = map(int, input().split())
C = list(map(lambda x: int(x)-1, input().split()))
D = list(map(lambda x: int(x)-1, input().split()))

Ss = [str(input()) for _ in range(H)]
group = [[-1 for _ in range(W)] for _ in range(H)]

moves = [[-1,0], [1,0], [0,-1], [0,1]]

from collections import deque
todo = deque()
now_group = -1
for i in range(H):
    for j in range(W):
        if group[i][j] == -1 and Ss[i][j]==".":
            todo.append([i,j])
            now_group += 1
            group[i][j] = now_group
        while len(todo) > 0:
            checking = todo.pop()
            for move in moves:
                now = [checking[0]+move[0],checking[1]+move[1]]
                if not (0 <= now[0] <H and 0 <= now[1] <W):
                    continue
                if group[now[0]][now[1]] == -1 and Ss[now[0]][now[1]]==".":
                    todo.append(now)
                    group[now[0]][now[1]] = now_group

can_waap = [set() for _ in range(now_group+1)]

for i in range(H):
    for j in range(W):
        if group[i][j] ==-1:
            continue
        for yoko in range(-2,3):
            for tate in range(-2,3):
                now = [tate+i, yoko+j]
                if not (0<=now[0]<H and 0<=now[1]<W):
                    continue
                if group[now[0]][now[1]] == -1:
                    continue
                
                if group[i][j] != group[now[0]][now[1]]:
                    can_waap[group[i][j]].add(group[now[0]][now[1]])
                    can_waap[group[now[0]][now[1]]].add(group[i][j])

start = group[C[0]][C[1]]
goal = group[D[0]][D[1]]
import sys
import copy
seen = set([start])
nows = [start]

if start==goal:
    print(0)
    sys.exit()
for step in range(now_group+1):
    pre_nows = copy.deepcopy(nows)
    nows = []
    for pre_now in pre_nows:
        for j in can_waap[pre_now]:
            if j not in seen:
                seen.add(j)
                nows.append(j)
                if j == goal:
                    print(step+1)
                    sys.exit()

print(-1)