Following information about a longwall retreating panel is given.

Panel length = 1800 m Face length = 150 m Depth of web = 0.6 m Shearer travels at a speed of 1.5 m/min along the face. Each cutting cycle requires a non-operational time of 2 h 20 min. The panel is fully extractable. The number of working days required to extract the panel is ______.