//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 list = new Array(H);
  var access = new Array(H);
  for(var i = 0; i < H; i++){
    list[i] = nextCharArray();
    access[i] = new Array(W).fill(false);
  }
  var output = -1;
  var warpQueue = new Array(H * W + 10);
  warpQueue[0] = [sy, sx];
  var warpMaeIndex = 0;
  var warpAtoIndex = 1;
  
  var dy = [-1,0,1,0];
  var dx = [0,-1,0,1];
  
  access[sy][sx] = true;
  var isFirst = false;
  while((warpMaeIndex != warpAtoIndex) || !isFirst){
    var warp = warpQueue[warpMaeIndex];
    var queue = new Array(H * W + 10);
    var maeIndex = 0;
    var atoIndex = 1;
    warpMaeIndex++;
    if(access[warp[0]][warp[1]] && isFirst){
      continue;
    }else{
      queue[0] = warp;
    }
    isFirst = true;
    output++;

    while(maeIndex != atoIndex){
      var now = queue[maeIndex];
      maeIndex++;
      var nowY = now[0];
      var nowX = now[1];
      if(nowY == ey && nowX == ex){
        myout(output);
        return;
      }
      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(!access[nextY][nextX]){
            if(list[nextY][nextX] == "."){
              queue[atoIndex] = [nextY, nextX];
              access[nextY][nextX] = true;
              atoIndex++;
            }
          }
        }
      }
      for(var i = nowY - 2; i <= nowY + 2; i++){
        for(var j = nowX - 2; j <= nowX + 2; j++){
          if(i >= 0 && i < H && j >= 0 && j < W){
            if(list[i][j] == "." && !access[i][j]){
              warpQueue[warpAtoIndex] = [i, j];
              warpAtoIndex++;
            }
          }
        }
      }
    }
    
  }
  
  myout(-1);
}