3. The sum of positive numbers $a, b, c$ and $d$ does not exceed 4. Find the maximum value of the expression

$$
\sqrt[4]{2 a^{2}+a^{2} b}+\sqrt[4]{2 b^{2}+b^{2} c}+\sqrt[4]{2 c^{2}+c^{2} d}+\sqrt[4]{2 d^{2}+d^{2} a}
$$