import sys
from collections import deque

def input(): return sys.stdin.readline().strip()

icase=0
if icase==0:
    h,w=map(int,input().split())
    ch,cw=map(int,input().split())
    ch-=1
    cw-=1
    dh,dw=map(int,input().split())
    dh-=1
    dw-=1
    s=[[] for i in range(h)]
    for i in range(h):
        s[i]=input()
        
ij=[(1,0),(-1,0),(0,1),(0,-1)]
wpij=[(1,1),(-1,-1),(-1,1),(1,-1),
      (2,-2),(2,-1),(2,0),(2,1),(2,2),
      (-2,-2),(-2,-1),(-2,0),(-2,1),(-2,2),
      (1,2),(0,2),(-1,2),(1,-2),(0,-2),(-1,-2)]

g=[[[] for i in range(w)] for i in range(h)]
gg=[[[] for i in range(w)] for i in range(h)]
wpg2=[[[0] for i in range(w)] for i in range(h)]
wpg=[]
for i in range(h):
    for j in range(w):
        ww=[]
        for ii,jj in ij:
            if 0>i+ii or i+ii>=h:
                continue
            if 0>j+jj or j+jj>=h:
                continue
            if s[i+ii][j+jj]==".":
                g[i][j].append((i+ii,j+jj))        
            else:
#                wpg.append((i,j))
                wpg2[i][j]=1
                
for i in range(h):
    for j in range(w):
        if wpg2[i][j]==1:
            wpg.append((i,j))
                
#wpg=tuple(set(wpg))

for i,j in wpg:
    for ii,jj in wpij:
         if 0<=i+ii and i+ii<h and 0<=j+jj \
            and j+jj<w and s[i+ii][j+jj]==".":
                gg[i][j].append((i+ii,j+jj))        

q=deque([(ch,cw)])
qq=deque()
parent=[[-1]*w for i in range(h)]
parent[ch][cw]=0
dist=[[-1]*w for i in range(h)]
dist[ch][cw]=0
while True:
    while q:
#        print("q1:",q)
        hi,wi = q.popleft()
        if len(gg[hi][wi])>0:
            qq.append((hi,wi))
        for hj,wj in g[hi][wi]:
            if parent[hj][wj] !=-1:
                continue
            else:
                parent[hj][wj]=(hi,wi)
                dist[hj][wj]=dist[hi][wi]+1
                q.append((hj,wj))
                if hj==dh and wj==dw:
                    print(dist[dh][dw]//(10**7))   
                    sys.exit()

    while qq:
        hi,wi = qq.popleft()
        for hj,wj in gg[hi][wi]:
            if parent[hj][wj]!=-1:
                continue
            parent[hj][wj]=(hi,wi)
            dist[hj][wj]=dist[hi][wi]+10**7
            q.append((hj,wj))
            if hj==dh and wj==dw:
                print(dist[dh][dw]//(10**7))   
                sys.exit()

    if len(q)==0:
        break
print(-1)   


### FIXED CODE ###


import sys
from collections import deque
import itertools

def input(): return sys.stdin.readline().strip()

icase=0
if icase==0:
    h,w=map(int,input().split())
    ch,cw=map(int,input().split())
    ch-=1
    cw-=1
    dh,dw=map(int,input().split())
    dh-=1
    dw-=1
    s=[[] for i in range(h)]
    for i in range(h):
        s[i]=input()
        
ij=[(1,0),(-1,0),(0,1),(0,-1)]
wpij=[(1,1),(-1,-1),(-1,1),(1,-1),
      (2,-2),(2,-1),(2,0),(2,1),(2,2),
      (-2,-2),(-2,-1),(-2,0),(-2,1),(-2,2),
      (1,2),(0,2),(-1,2),(1,-2),(0,-2),(-1,-2)]

hh=[i for i in range(h)]
ww=[i for i in range(w)]

g=[[[] for i in range(w)] for i in range(h)]
gg=[[[] for i in range(w)] for i in range(h)]
wpg2=[[0]*w for i in range(h)]
wpg=[]

hhww=[(i,j) for i,j in itertools.product(hh,ww) if s[i][j]=="."]
                
for i,j in hhww:
    g[i][j]=[(i+ii,j+jj) for ii,jj in ij if (0<=(i+ii)<h and 0<=(j+jj)<w and s[i+ii][j+jj]==".")] 
    if i+1<h and s[i+1][j]=="#": wpg2[i][j]=1
    elif 0<=i-1 and s[i-1][j]=="#": wpg2[i][j]=1
    elif j+1<w and s[i][j+1]=="#": wpg2[i][j]=1
    elif 0<=j-1 and s[i][j-1]=="#": wpg2[i][j]=1

for i,j in hhww:
    if wpg2[i][j]>=1:
        wpg.append((i,j))
                
for i,j in wpg:
    for ii,jj in wpij:
         if 0<=i+ii and i+ii<h and 0<=j+jj \
            and j+jj<w and s[i+ii][j+jj]==".":
                gg[i][j].append((i+ii,j+jj))        

q=deque([(ch,cw)])
qq=deque()
parent=[[-1]*w for i in range(h)]
parent[ch][cw]=0
dist=[[-1]*w for i in range(h)]
dist[ch][cw]=0
while True:
    while q:
#        print("q1:",q)
        hi,wi = q.popleft()
        if len(gg[hi][wi])>0:
            qq.append((hi,wi))
        for hj,wj in g[hi][wi]:
            if parent[hj][wj] !=-1:
                continue
            else:
                parent[hj][wj]=(hi,wi)
                dist[hj][wj]=dist[hi][wi]+1
                q.append((hj,wj))
                if hj==dh and wj==dw:
                    print(dist[dh][dw]//(10**7))   
                    sys.exit()

    while qq:
        hi,wi = qq.popleft()
        for hj,wj in gg[hi][wi]:
            if parent[hj][wj]!=-1:
                continue
            parent[hj][wj]=(hi,wi)
            dist[hj][wj]=dist[hi][wi]+10**7
            q.append((hj,wj))
            if hj==dh and wj==dw:
                print(dist[dh][dw]//(10**7))   
                sys.exit()

    if len(q)==0:
        break
print(-1)