import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Random;
import java.util.StringTokenizer;

public class Main {

    static int h, w;
    static char[][] board;

    public static void main(String[] args) {
        FastScanner fs=new FastScanner();
        h=fs.nextInt(); w=fs.nextInt();
        int sy=fs.nextInt()-1, sx=fs.nextInt()-1;
        int ey=fs.nextInt()-1, ex=fs.nextInt()-1;
        ArrayDeque<Integer> xs=new ArrayDeque<>(), ys=new ArrayDeque<>();
        board=new char[w][h];
        for (int y=0; y<h; y++) {
            char[] line=fs.next().toCharArray();
            for (int x=0; x<w; x++) {
                board[x][y]=line[x];
            }
        }
        xs.add(sx);
        ys.add(sy);
        int[][] dist=new int[w][h];
        for (int x=0; x<w; x++) Arrays.fill(dist[x], 1_000_000_000);
        dist[sx][sy]=0;
        int[] dx= {-1, 1, 0, 0};
        int[] dy= {0, 0, -1, 1};
        while (!xs.isEmpty()) {
            int curX=xs.removeFirst(), curY=ys.removeFirst();
            for (int d=0; d<4; d++) {
                int nx=curX+dx[d], ny=curY+dy[d];
                if (!legal(nx, ny)) continue;
                if (dist[nx][ny]>dist[curX][curY]) {
                    dist[nx][ny]=dist[curX][curY];
                    xs.addFirst(nx);
                    ys.addFirst(ny);
                }
            }
            for (int x=curX-2; x<=curX+2; x++) {
                for (int y=curY-2; y<=curY+2; y++) {
                    if (!legal(x, y)) continue;
                    if (dist[x][y]>dist[curX][curY]+1) {
                        dist[x][y]=dist[curX][curY]+1;
                        xs.addLast(x);
                        ys.addLast(y);
                    }
                }
            }
        }
        System.out.println(dist[ex][ey]>1e7?-1:dist[ex][ey]);
    }

    static boolean legal(int x, int y) {
        if (x<0||y<0||x>=w||y>=h || board[x][y]=='#') return false;
        return true;
    }

    static final Random random=new Random();

    static void ruffleSort(int[] a) {
        int n=a.length;//shuffle, then sort
        for (int i=0; i<n; i++) {
            int oi=random.nextInt(n), temp=a[oi];
            a[oi]=a[i]; a[i]=temp;
        }
        Arrays.sort(a);
    }

    static class FastScanner {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st=new StringTokenizer("");
        String next() {
            while (!st.hasMoreTokens())
                try {
                    st=new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }
        int[] readArray(int n) {
            int[] a=new int[n];
            for (int i=0; i<n; i++) a[i]=nextInt();
            return a;
        }
        long nextLong() {
            return Long.parseLong(next());
        }
    }


}