map = {};
for (y = 2; y <= Bottom; y++) {
  key = [3,y];
  if (key != "") {
    map[key] = {};
    for (x = 4; x <= Right; x++) {
      map[key][x] = [x,y];
    }
  }
}

for (y = 2; y <= Bottom; y++) {
  key = [1,y];
  if (key in map) {
    [3,y] = key;
    for (x = 4; x <= Right; x++) {
      [x,y] = map[key][x];
    }
  } else {
    [3,y] = "";
    for (x = 4; x <= Right; x++) {
      [x,y] = "";
    }
  }
}