An industry has 3 firms (1, 2 and 3) in Cournot competition. They have no fixed costs, and their constant marginal costs are respectively\(c_1=\frac{9}{30} , π_2 =\frac{ 10}{30} , π_3 = \frac{11}{30} .\)
They face an industry inverse demand function π=1βπ, where π is the market price and π is the industry output (sum of outputs of the 3 firms). Suppose that π π is the industry output under Cournot-Nash equilibrium. Then (π π )β1 is equal to _______ (in integer).