The following "prisoners' dilemma" game is repeated an infinite number of times. Both players discount future payoffs at a common discount rate < 1. Cooperate Defect Cooperate Defect Consider the "grim trigger" strategy profile in which both players choose Cooperate in the first period, and continue to cooperate as long as no player has ever chosen Defect. What is the lowest level of that could sustain this strategy profile as a subgame perfect Nash equilibrium? Enter your answer to two decimal places.