The overall stability constant

Question:
The overall stability constant of the complex ion $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}$ is $2.1 \times 10^{13}$. The overall dissociations constant is $\mathrm{y} \times 10^{-14}$. Then $\mathrm{y}$ is .(Nearest integer)

Solution:

Given $\mathrm{k}_{\mathrm{f}}=2.1 \times 10^{13}$