Please reason step by step, and put your final answer within \boxed{}.

A field is a $41 \times 41$ grid, and a tank is hidden in one of the cells. A fighter plane fires at one cell at a time. If the shot hits, the tank moves to an adjacent cell (sharing a side); if the shot misses, the tank remains in place. After each shot, the pilot does not know if the shot was a hit or miss. To destroy the tank, it must be hit twice. What is the minimum number of shots needed to guarantee that the tank is destroyed?
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