multi decider combinator with only one exit

[_Ax_]

Hi, I'm trying to make a system that if station 1 is free returns one, if the second is free returns 2. But if station 1 and 2 are free returns first 1 and when station 1 is occuped returns 2 etc. But I don't know how to make that only one combinator output can go when all other outputs of all other combinators are bocked.

Like:
0 = no output
N = station number
each number represents a combinator (except for 0 that means no output from that combinator)

1 2 3 returns 1
0 2 3 returns 2
0 0 3 returns 3
0 2 0 returns 2

But I don't know how to do it with decider combinator, any help?

[DaveMcW]

viewtopic.php?p=250107#p250107

[_Ax_]

viewtopic.php?p=250107#p250107

Yeah but I have to output the same signal. The dispatcher signal (of a mod) to make that the train will go to the free station. I want to make that it will go in numerical order. 1, 2, 3, etc of free stations : D