from heapq import heappush, heappop
from collections import deque

def solve():
    H,W = map(int,input().split())
    sx,sy = map(lambda x:int(x)-1, input().split())
    gx,gy = map(lambda x:int(x)-1, input().split())
    A = [list(input().rstrip()) for _ in range(H)]
    dx = gx - sx
    dy = gy - sy

    vis = [[False]*W for _ in range(H)]
    dq = deque([(sx,sy)])
    vis[sx][sy] = True
    while dq:
        x,y = dq.popleft()
        for dxx,dyy in ((1,0),(-1,0),(0,1),(0,-1)):
            nx,ny = x+dxx, y+dyy
            if 0<=nx<H and 0<=ny<W and not vis[nx][ny] and A[nx][ny] != '#':
                vis[nx][ny] = True
                dq.append((nx,ny))

    if not vis[gx][gy]:
        print(-1)
        return

    pareto = [[[] for _ in range(W)] for __ in range(H)]
    pq = [(0,0,0,sx,sy)]
    pareto[sx][sy].append((0,0))
    while pq:
        _, v, h, x, y = heappop(pq)
        dominated = False
        for vv,hh in pareto[x][y]:
            if vv<=v and hh<=h and (vv,hh)!=(v,h):
                dominated = True; break
        if dominated: continue

        for dxx,dyy in ((1,0),(-1,0),(0,1),(0,-1)):
            nx,ny = x+dxx, y+dyy
            if not (0<=nx<H and 0<=ny<W and A[nx][ny] != '#'): continue
            nv, nh = v + (1 if dxx!=0 else 0), h + (1 if dyy!=0 else 0)
            skip = False
            remove = []
            for idx,(vv,hh) in enumerate(pareto[nx][ny]):
                if vv<=nv and hh<=nh:
                    skip = True; break
                if nv<=vv and nh<=hh:
                    remove.append(idx)
            if skip: continue
            for idx in reversed(remove):
                pareto[nx][ny].pop(idx)
            pareto[nx][ny].append((nv,nh))
            heappush(pq, (nv+nh, nv, nh, nx, ny))

    MAXP = 200000
    is_prime = [True]*(MAXP+1)
    is_prime[0]=is_prime[1]=False
    for i in range(2,MAXP+1):
        if is_prime[i]:
            for j in range(i+i, MAXP+1, i):
                is_prime[j] = False

    def min_pad(big, small):
        for t in range(0, MAXP-big+1):
            if big == 0 and t != 0:
                break
            p = big + t
            q = small + t
            if q<2: continue
            if is_prime[p] and is_prime[q]:
                return t
        return None

    ans = None
    for V,H in pareto[gx][gy]:

        assert not (V<abs(dx) or (V-dx)%2!=0)
        assert not (H<abs(dy) or (H-dy)%2!=0)

        A0 = (V + dx)//2
        B0 = (V - dx)//2
        C0 = (H + dy)//2
        D0 = (H - dy)//2

        pad_v = min_pad(max(A0,B0), min(A0,B0))
        pad_h = min_pad(max(C0,D0), min(C0,D0))
        if pad_v is None or pad_h is None:
            continue

        total = (V+H) + 2*pad_v + 2*pad_h
        if ans is None or total<ans:
            ans = total

    print(ans if ans is not None else -1)
solve()

"""
2 3
2 2
2 3
.##
.SG
"""