  We propose a phenomenological formula relating the
Cabibbo--Kobayashi--Masukawa matrix $V_{CKM}$ and quark masses in the form
$(\sqrt{m_d} \, \sqrt{m_s} \, \sqrt{m_b}) \propto (\sqrt{m_u} \, \sqrt{m_c} \,
\sqrt{m_t})V_{CKM}$. The results of the proposed formula are in agreement with
experimental data. Under the constraint of the formula, we show that the
invariant amplitude of the charged current weak interactions is maximized.
