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]:

        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


    dist0 = [[-1]*W for _ in range(H)]
    parent = [[None]*W for _ in range(H)]
    dq2 = deque([(sx,sy)])
    dist0[sx][sy] = 0
    while dq2:
        x,y = dq2.popleft()
        for dx_,dy_,op in ((1,0,'A'),(-1,0,'B'),(0,1,'C'),(0,-1,'D')):
            nx,ny = x+dx_, y+dy_
            if 0<=nx<H and 0<=ny<W and A[nx][ny] != '#' and dist0[nx][ny] < 0:
                dist0[nx][ny] = dist0[x][y] + 1
                parent[nx][ny] = (x,y,op)
                dq2.append((nx,ny))
    A1=B1=C1=D1 = 0
    path = []
    cx,cy = gx,gy
    while (cx,cy) != (sx,sy):
        path.append((cx,cy))
        px,py,op = parent[cx][cy]
        if   op=='A': A1 += 1
        elif op=='B': B1 += 1
        elif op=='C': C1 += 1
        else:         D1 += 1
        cx,cy = px,py
    path.append((sx,sy))

    if not ( (A1+B1>0) and (C1+D1>0) ):
        assert False
        d2 = [[-1]*W for _ in range(H)]
        dq3 = deque(path)
        for x,y in path:
            d2[x][y] = 0
        while dq3:
            x,y = dq3.popleft()
            for dx_,dy_ in ((1,0),(-1,0),(0,1),(0,-1)):
                nx,ny = x+dx_, y+dy_
                if 0<=nx<H and 0<=ny<W and A[nx][ny] != '#' and d2[nx][ny]<0:
                    d2[nx][ny] = d2[x][y] + 1
                    dq3.append((nx,ny))

        # 5) 縦移動ペア＆横移動ペアまでの最小距離を探す
        INF = 10**9
        best_v = INF
        for i in range(H-1):
            for j in range(W):
                if A[i][j] != '#' and A[i+1][j] != '#':
                    # path→(i,j) or (i+1,j) の距離
                    for (ii,jj) in ((i,j),(i+1,j)):
                        if d2[ii][jj]>=0:
                            best_v = min(best_v, d2[ii][jj])
        best_h = INF
        for i in range(H):
            for j in range(W-1):
                if A[i][j] != '#' and A[i][j+1] != '#':
                    for (ii,jj) in ((i,j),(i,j+1)):
                        if d2[ii][jj]>=0:
                            best_h = min(best_h, d2[ii][jj])

        # 6) 欠けている方向だけ往復２手を入れて candidate を作る
        base0 = A1 + B1 + C1 + D1  # 最短路長
        extra = 0
        # 縦移動ゼロなら
        if A1+B1 == 0:
            if best_v < INF:
                extra += 2*best_v + 4
            else:
                extra = INF
        # 横移動ゼロなら
        if C1+D1 == 0:
            if best_h < INF:
                extra += 2*best_h + 4
            else:
                extra = INF
        if extra < INF:
            ans = base0 + extra if ans is None else min(ans, base0 + extra)



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

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