\[ \boxed { {\it d4y} \left ( x \right ) =0} \]
Mathematica: cpu = 0.003000 (sec), leaf count = 24 \[ \left \{\left \{y(x)\to c_4 x^3+c_3 x^2+c_2 x+c_1\right \}\right \} \]
Maple: cpu = 0.141 (sec), leaf count = 21 \[ \left \{ y \left ( x \right ) ={\frac {{\it \_C1}\,{x}^{3}}{6}}+{\frac { {\it \_C2}\,{x}^{2}}{2}}+{\it \_C3}\,x+{\it \_C4} \right \} \]