At 500°C the Equilibrium Constant, K_p , Is 4

At 500°C the equilibrium constant, K_p , is 4.00 × 10^-4 for the equilibrium: 2HCN(g) H₂(g) + C₂N₂(g)
What is K_p for the following reaction?
H₂(g) + C₂N₂(g) 2HCN(g)

A) 2.00 × 10^-4
B) -4.00 × 10^-4
C) 1.25 × 10³
D) 2.50 × 10³
E) 4.00 × 10⁴