20

:

2

=

10

18

:

2

=

9

16

:

2

=

8

14

:

2

=

7

12

:

2

=

6

10

:

2

=

5

8

:

2

=

4

6

:

2

=

3

4

:

2

=

2

2

:

2

=

1