\[ \boxed { \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) \left ( 1+\sin \left ( x \right ) \right ) \sin \left ( y \left ( x \right ) \right ) +\cos \left ( x \right ) \left ( \cos \left ( y \left ( x \right ) \right ) -1 \right ) =0} \]
Mathematica: cpu = 0.117515 (sec), leaf count = 32 \[ \left \{\{y(x)\to 0\},\left \{y(x)\to 2 \sin ^{-1}\left (\frac {1}{4} c_1 \left (\sin \left (\frac {x}{2}\right )+\cos \left (\frac {x}{2}\right )\right )\right )\right \}\right \} \]
Maple: cpu = 0.094 (sec), leaf count = 16 \[ \left \{ y \left ( x \right ) =\pi -\arccos \left ( \sin \left ( x \right ) {\it \_C1}+{\it \_C1}-1 \right ) \right \} \]