#include<iostream>
#include<cstdio>
#include<queue>
using namespace std;

int n,m,x1,y1,x2,y2;
char map[503][503];
int step[503][503];
bool vis[503][503];
int dx[]={0,1,0,-1};
int dy[]={1,0,-1,0};

inline void bfs(){
    queue<pair<int,int> >q;
    q.push(make_pair(x1,y1));
    step[x1][y1]=0;
    vis[x1][y1]=1;

    while(q.size()){
        int x=q.front().first,
            y=q.front().second;
            q.pop();
        for(register int i=0;i<4;++i){
            int xx=x+dx[i];
            int yy=y+dy[i];   
            if(xx<0||xx>n||yy<0||yy>m||vis[xx][yy])
                continue;

            if(map[xx][yy]!=map[x][y])
                step[xx][yy]=step[x][y]+1;
            else step[xx][yy]=step[x][y];  
			if(xx==x2&&yy==y2)return; 
			
            q.push(make_pair(xx,yy));
            vis[xx][yy]=1;     
        }
    }
}

int main(){
    while(1){
        scanf("%d%d",&n,&m);
        if(n==0&&m==0)break;
        for(register int i=0;i<n;++i)
            for(register int j=0;j<m;j++){
				step[i][j]=0;
                cin>>map[i][j];
			}
        scanf("%d%d%d%d",&x1,&y1,&x2,&y2);        
        bfs();
        printf("%d\n",step[x2][y2]);
    }
    return  0;
}