Quadratic Equation And Inequalities

Let $\alpha, \alpha+2, \alpha \in \mathbf{Z}$, be the roots of the quadratic equation $x(x+2)+(x+1)(x+3)+(x+2)(x+4)+\ldots .+(x+\mathrm{n}-1)(x+\mathrm{n}+1)=4 \mathrm{n}$ for some $\mathrm{n} \in \mathbf{N}$. Then $\mathrm{n}+\alpha$ is equal to :