Let f : R→R be a twice differentiable function such that the quadratic equation f(x)m² – 2f '(x)m + f''(x)=0 in m, has two equal roots for every x∈R. If f(0)=1, f '(0) = 2 and (α, β) is the largest interval in which the function f(log_e x – x) is increasing, then α + β is equal to