//Don't have to see. start------------------------------------------
var read = require('readline').createInterface({
  input: process.stdin, output: process.stdout
});
var obj; var inLine = [];
read.on('line', function(input){inLine.push(input);});
read.on('close', function(){
  obj = init(inLine);
  console.error('\n↑入力 ↓出力');
  Main();
});
function makeClone(obj){return (obj instanceof Set) ? new Set(Array.from(obj)) : JSON.parse(JSON.stringify(obj));}
function nextInt(){return myconv(next(),1);} function nextStrArray(){return myconv(next(),2);}
function nextIntArray(){return myconv(next(),4);} function nextCharArray(){return myconv(next(),6);}
function next(){return obj.next();} function hasNext(){return obj.hasNext();}
function init(input){  
  return {
    list : input, index : 0, max : input.length,
    hasNext : function(){return (this.index < this.max);},
    next : function(){if(this.hasNext()){return this.list[this.index++];}else{throw 'ArrayIndexOutOfBoundsException ‚There is no more input';}}
  };
}
function myout(s){console.log(s);}
function myerr(s){console.error('debug:' + require('util').inspect(s,false,null));}
//param "no" is
//unknown or outlier : return i. 1: parseInt.
//2: split space. 4: split space and parseInt.
//6: split 1 character. 7: split 1 character and parseInt.
//8: join space. 9: join nextline. 0: join no character.
function myconv(i,no){try{switch(no){case 1:return parseInt(i);case 2:return i.split(' ');case 4:return i.split(' ').map(Number);case 6:return i.split('');case 7:return i.split('').map(Number);case 8:return i.join(' ');case 9:return i.join('\n');case 0:return i.join('');default:return i;}}catch(e){return i;}}

//Don't have to see. end------------------------------------------
function Main(){
  var one = nextIntArray();
  var H = one[0];
  var W = one[1];
  one = nextIntArray();
  var sy = one[0] - 1;
  var sx = one[1] - 1;
  one = nextIntArray();
  var ey = one[0] - 1;
  var ex = one[1] - 1;
  var dy = [-1,0,1,0];
  var dx = [0,-1,0,1];
  var list = new Array(H);
  for(var i = 0; i < H; i++){
    list[i] = new Array(W);
    var tmp = nextCharArray();
    for(var j = 0; j < W; j++){
      list[i][j] = {
        s : tmp[j],
        access : false,
        group : -1,
      };
    }
  }
  var group = 0;
  for(var i = 0; i < H; i++){
    for(var j = 0; j < W; j++){
      if(!list[i][j].access && list[i][j].s == "."){
        list[i][j].group = group;
        group++;
        bfs(i, j);
      }
    }
  }
  
  
  var groupList = new Array(group);
  for(var i = 0; i < group; i++){
    groupList[i] = {
      child : new Set(),
      access : false,
      count : 0
    };
  }
  
  for(var i = 0; i < H; i++){
    for(var j = 0; j < W; j++){
      if(list[i][j].s == "."){
        for(var k = i - 2; k <= i + 2; k++){
          for(var l = j - 2; l <= j + 2; l++){
            if(k >= 0 && k < H && l >= 0 && l < W){
              if(list[k][l].s == "." && list[k][l].group != list[i][j].group){
                groupList[list[k][l].group].child.add(list[i][j].group);
                groupList[list[i][j].group].child.add(list[k][l].group);
              }
            }
          }
        }
      }
    }
  }

  var groupQueue = [list[sy][sx].group];
  while(groupQueue.length > 0){
    var nowGroup = groupQueue.shift();
    if(nowGroup == list[ey][ex].group){
      myout(groupList[nowGroup].count);
      return;
    }
    var child = Array.from(groupList[nowGroup].child);
    for(var i = 0; i < child.length; i++){
      if(!groupList[child[i]].access){
        groupList[child[i]].access = true;
        groupList[child[i]].count = groupList[nowGroup].count + 1;
        groupQueue.push(child[i]);
      }
    }
  }
  myout(-1);
  function bfs(y, x){
    var queue = [[y, x]];
    list[y][x].access = true;
    while(queue.length > 0){
      var now = queue.shift();
      var nowY = now[0];
      var nowX = now[1];
      for(var i = 0; i < dy.length; i++){
        var nextY = nowY + dy[i];
        var nextX = nowX + dx[i];
        if(nextY >= 0 && nextY < H && nextX >= 0 && nextX < W){
          if(!list[nextY][nextX].access && list[nextY][nextX].s == "."){
            queue.push([nextY, nextX]);
            list[nextY][nextX].group = list[nowY][nowX].group;
            list[nextY][nextX].access = true;
          }
        }
      }
    }
  }
}

Measured memory_bytes: 160228