I have the following model:

............A........B
1.........1........blank
2.........2........a
3.........3........a
4.........4........1
5.........5........2
6.........6........blank
7.........7........b
8.........8........blank
9.........9........1

In C1 I have:
=IF(COUNTIF($B$1:B1;B1)=1;A1;10)
which I copy down to C9

In D1 I have:
=SMALL($C$1:$C$9;A1)
which I copy down to D9

In this D column I get:
2
4
5
7
10
10
10
10
10
which is what I want.

However, combining the two formulas into one does not work. I've tried
in E1:
=SMALL(IF(COUNTIF($B$1:B1;B1)=1;A1;10):A1) which I copy down to E9

I get:
10
#NUM!
#NUM!
#NUM!
#NUM!
#NUM!
#NUM!
#NUM!
#NUM!

Nothing to do with the desired result. I have no idea why it doesn't
work.

Any help?