\[\boxed{\text{664\ (664).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[b^{2} + \frac{a^{2}}{4} = 1;\ \ ab = 3;\ \ \]
\[a > 0;\ \ b > 0\]
\[\left( b + \frac{a}{2} \right)^{2} = 4,\ \ \]
\[b + \frac{a}{2} = 2\ \ \ \ \ | \cdot 2\]
\[2b + a = 4\]
\[Ответ:4.\]