B. Given that $a$ is an integer. If there exist two unequal integers $x, y$ satisfying the system of equations $\left\{\begin{array}{l}x-y^{2}=a, \\ y-x^{2}=a,\end{array}\right.$ and $|x| \leqslant 10$, then the minimum value of $a$ is . $\qquad$