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2 of 2 deleted 1 character in body

QBIC, 27 26 bytes

g=(:+1)'\2`~(a-g)%2|?-g\?g

Explanation

g=          set worker var 'g' to
(:+1)           our index (plus one for the ceil() bit)
'\2`            integer divided by 2 (the int div needs a code literal: '..`
~(a-g)%2    IF index - temp result is odd (index 2 minus result 1 = 1)
|?-g        THEN PRINT g negated
\?g         ELSE PRINT g