alternate cycle

question:

fix 1
run 1000 upto

unfix 1
fix 2
run 2000 upto

unfix 2
fix 1
run 3000 upto

unfix 1
fix 2
run 4000 upto

unfix 2
fix 1
run 5000 upto

repeat ..

I want to know what command or skills may use for the alternate cycle as above example. Welcome any suggestion or advise.

thank you in advance.

best regards,
xinze