Stack

Vertical stack:

1

2

3

4

5

6

1

2

3

4

5

6

1

2

3

4

5

6

Horizontal stack:

1

2

3

4

5

6

1

2

3

4

5

6

1

2

3

4

5

6

1

2

3

4

5

6

1

2

3

4

5

6

1

2

3

4

5

6

1

2

3

4

5

6

1

2

3

4

5

6

1

2

3

4

5

6