\[ \boxed { {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) -{{\rm e}^{x-y \left ( x \right ) }}+{{\rm e}^{x}}=0} \]
Mathematica: cpu = 0.191024 (sec), leaf count = 20 \[ \left \{\left \{y(x)\to \log \left (1-e^{c_1-e^x}\right )\right \}\right \} \]
Maple: cpu = 0.109 (sec), leaf count = 20 \[ \left \{ y \left ( x \right ) =-{{\rm e}^{x}}+\ln \left ( -1+{{\rm e}^{{ {\rm e}^{x}}+{\it \_C1}}} \right ) -{\it \_C1} \right \} \]