7. Let $a, b, c$ be three distinct real numbers such that the equations $x^{2}+a x+1=0$ and $x^{2}+b x+c=0$ have a common real root, and the equations $x^{2}+x+a=0$ and $x^{2}+c x+b=0$ also have a common real root, then the value of $a+b+c$ is $\qquad$.