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 × 10 ³
D) 2.50 × 10 ³
E) 4.00 × 10 ⁴