If ${\sin }^{-1}x+{\sin }^{-1}y=\frac{2\pi }{3}$ then ${\cos }^{-1}x+{\cos }^{-1}y$ is 

Mark the tick against the correct answer in the following:

${\tan }^{-1}1+{\cos }^{-1}\left(\frac{-1}{2}\right)+{\sin }^{-1}\left(\frac{-1}{2}\right)=?$