Red Army and Blue Army must decide whether to attack or defend their territories. The decisions are made without the knowledge of the opposing army's decision in this zero-sum game. The Red Army will gain 3 territories if both armies decide to attack. The Red Army will gain 5 territories if it decides to attack and the Blue Army decides to defend. On the other hand, the Red Army will gain 4 territories if it decides to defend and the Blue Army decides to attack. The Red Army will gain nothing if both armies decide to defend their territories. What is the optimal strategy for each army ?