Consider the following grid. The symbols C indicates a cliff and r1 indicates that 50 units of resource r1 have appeared at time 0. We suppose that no other resource appear later on.

A robot starts in the location marked with (but does not know where C and r1 are). Its absolute priority is to not fall from a cliff. Moreover, the robot knows the two following facts:

• For every location that is a cliff, there is an adjacent location that is flat and contains some non null quantity of resource r1.

• For every location that is flat and contains some non null quantity of resource r1, exactly one adjacent location is a cliff.

We also remind that the robot can feel if there is a cliff on an adjacent location (but does not know on which location exactly). Also, the resource decreases per unit time. What is the maximal quantity of resources that the robot can collect without risking to fall from a cliff?

6 r1 Cri 5 C 4 ri Cri 3 N 2 Cri 1 1 2 3 4 5 6