Formation of sodium acetylide

Treatment of buta-$$1,3$$-diyne with $$NaNH_2$$ ($$2$$ equivalents), followed by reaction with excess of trans-$$CH_3\text{-}CH\!=\!CH\text{-}CH_2\text{-}Br$$ gives $$\mathbf{X}$$ as the major product. The maximum number of carbon atoms that are collinear (in a straight line) in $$\mathbf{X}$$ is ___.