/*****
题意：给出一个矩阵，然后给出两个点，让求链接这两个点需要打的洞的最小值
          ‘.’代表空位置，‘X’代表是洞；
做法：bfs + 优先队列
*****/
#include<iostream>
#include<string.h>
#include<algorithm>
#include<cmath>
#include<stdio.h>
#include<queue>
using namespace std;
#define maxn 1100
#define INF 1000000
int Edge[maxn][maxn];
char ch[maxn][maxn];
int dx[4] = {0,0,-1,1};
int dy[4] = {1,-1,0,0,};
int n,m;
int temp = 0;
int sx,sy,ex,ey;
int vis[maxn][maxn];
struct Node
{
    int x;
    int y;
    int step;
    Node()
    {
        x = 0;
        y = 0;
        step =0;
    }
};
struct cmp
{
    bool operator () (const Node &a,const Node &b)
    {
        return a.step>b.step;
    }
};
int  check(Node a)
{
    if(a.x >= 1 && a.x <=n && a.y>=1 && a.y <=m) return 1;
    return 0;
}
priority_queue<Node,vector<Node>,cmp >que;
int bfs()
{
    while(!que.empty()) que.pop();
    Node now,tmp;
    now.x = sx;
    now.y = sy;
    now.step = 0;
    que.push(now);
    vis[sx][sy] = 1;
    while(!que.empty())
    {
        tmp = que.top();
        que.pop();
        if(tmp.x == ex && tmp.y == ey) return tmp.step;
        for(int i=0; i<4; i++)
        {
            now.x = tmp.x + dx[i];
            now.y = tmp.y + dy[i];
            if(check(now) && vis[now.x][now.y] == 0)
            {
                if(Edge[now.x][now.y] == 0) now.step = tmp.step;
                else
                {
                    now.step = tmp.step + 1;
                }
                que.push(now);
                vis[now.x][now.y] = 1;
            }
        }
    }
}

int main()
{
//#ifndef ONLINE_JUDGE
//    freopen("in1.txt","r",stdin);
//#endif
    while(~scanf("%d %d",&n,&m))
    {
        if(n == 0 && m == 0) break;
        memset(Edge,INF,sizeof(Edge));
        memset(vis,0,sizeof(vis));
        for(int i=1; i<=n; i++)
        {
            scanf("%s",ch[i]);
            for(int j=0; j<m; j++)
            {
                if(ch[i][j] == ‘X‘) Edge[i][j+1] = 0;
            }
        }
        getchar();
        for(int i=1; i<=n; i++)
        {
            for(int j=1; j<=m; j++)
            {
                if(Edge[i][j] == 0) continue;
                Edge[i][j] = min(Edge[i-1][j],min(Edge[i+1][j],min(Edge[i][j-1],Edge[i][j+1]))) + 1;
            }
        }
        temp = 0;
        scanf("%d %d",&sx,&sy);
        scanf("%d %d",&ex,&ey);
        getchar();
        int temp = bfs();
        printf("%d\n",temp);
    }
    return 0;
}