Complex Numbers

If $z_{1}, z_{2}, z_{3}$ are three complex numbers with unit modulus such that $\left|z_{1}-z_{2}\right|^{2}+\left|z_{1}-z_{3}\right|^{2}=4$, then $z_{1} \bar{z}_{2}+\bar{z}_{1} z_{2}+z_{1} \bar{z}_{3}+\bar{z}_{1} z_{3}=$