Let $\bar{a}, \bar{b}, \bar{c}$ be three vectors such that $\overline{\mathrm{a}}+\overline{\mathrm{b}}+\overline{\mathrm{c}}=\overline{0},|\overline{\mathrm{a}}|=3,|\overline{\mathrm{~b}}|=4,|\overline{\mathrm{c}}|=5$, then $\overline{\mathrm{a}} \cdot \overline{\mathrm{b}}+\overline{\mathrm{b}} \cdot \overline{\mathrm{c}}+\overline{\mathrm{c}} \cdot \overline{\mathrm{a}}=$