The floor is not slippery

$\large \left | x^2 - \left \lfloor \frac{x+1} 2\right \rfloor \right | = 4000$

Find the unique solution of $x$ satisfying the equation above.

If you think that there isn't a unique solution, submit your answer as -1.

Notations:

• $| \cdot |$ denotes the absolute value function .

• $\lfloor \cdot \rfloor$ denotes the floor function .