from collections import deque
from bisect import bisect_left
H,W=map(int,input().split())
sx,sy=map(int,input().split())
gx,gy=map(int,input().split())
S=["#"*(W+2) for i in range(H+2)]
for i in range(H):
    S[i+1]="#"+input()+"#"
S=[list(s) for s in S]
S[sx][sy]="."
S[gx][gy]="."
H+=2
W+=2
num=[[0]*W for i in range(H)]
for i in range(1,H-1):
    for j in range(1,W-1):
        if S[i-1][j]=="." or S[i+1][j]==".":
            num[i][j]^=1
        if S[i][j-1]=="." or S[i][j+1]==".":
            num[i][j]^=2
dist=[[[[1<<60]*4 for i in range(2000)] for i in range(W)] for i in range(H)]
dist[sx][sy][0][num[sx][sy]]=0
vert=deque()
vert.append((0,sx,sy,0,num[sx][sy]))
while vert:
    d,x,y,r,b=vert.popleft()
    if dist[x][y][r][b]!=d:
        continue
    if S[x+1][y]==".":
        if dist[x+1][y][r][b|num[x+1][y]]>d+1:
            dist[x+1][y][r][b|num[x+1][y]]=d+1
            vert.append((d+1,x+1,y,r,b|num[x+1][y]))
    if S[x-1][y]==".":
        if dist[x-1][y][r][b|num[x-1][y]]>d:
            dist[x-1][y][r][b|num[x-1][y]]=d
            vert.appendleft((d,x-1,y,r,b|num[x-1][y]))
    if S[x][y+1]==".":
        if r!=1999 and dist[x][y+1][r+1][b|num[x][y+1]]>d:
            dist[x][y+1][r+1][b|num[x][y+1]]=d
            vert.appendleft((d,x,y+1,r+1,b|num[x][y+1]))
    if S[x][y-1]==".":
        if dist[x][y-1][r][b|num[x][y-1]]>d:
            dist[x][y-1][r][b|num[x][y-1]]=d
            vert.appendleft((d,x,y-1,r,b|num[x][y-1]))
swx=gx-sx
swy=gy-sy
X=50000
primes=[1]*X
primes[0]=0
primes[1]=0
for i in range(2,X):
    if primes[i]==0:
        continue
    for j in range(i*2,X,i):
        primes[j]=0
px=[]
py=[]
for i in range(X):
    if 0<=i-swx<X and primes[i] and primes[i-swx]:
        px.append(i)
for i in range(X):
    if 0<=i-swy<X and primes[i] and primes[i-swy]:
        py.append(i)
px.append(1<<60)
py.append(1<<60)
ans=1<<60
for i in range(2000):
    ans=min(ans,(py[bisect_left(py,dist[gx][gy][i][3])]+px[bisect_left(px,i)])*2+swx+swy)
if ans>=(1<<60):
    print(-1)
else:
    print(ans)