1. For the complex formation

$Cu^{2+} + 4NH_3 \rightleftharpoons [Cu(NH_3)_4]^{2+}$

the overall stability constant is

$\beta_4 = \frac{[Cu(NH_3)_4^{2+}]}{[Cu^{2+}][NH_3]^4} = 2.1 \times 10^{13}$

2. The overall dissociation constant is the reciprocal of the stability constant:

$K_d = \frac{1}{\beta_4}$

So,

$K_d = \frac{1}{2.1 \times 10^{13}}$

3. Calculate it:

$K_d = \frac{1}{2.1} \times 10^{-13}$

$K_d \approx 0.476 \times 10^{-13}$

$K_d = 4.76 \times 10^{-14}$

4. Comparing with the given form:

$K_d = y \times 10^{-14}$

we get

$y = 4.76$

Nearest integer:

$y = 5$

Therefore, the required integer is 5.