A Viable model for modified gravity

We propose a model for modified gravity that meets the conditions of viability. The model has stable constant curvature solution and for an special case contains flat space time solution. The model also leads to matter stability under small perturbations of scalar curvature. We give an example of restrictions on the parameters that give large enough scalaron mass to avoid detectable corrections to the Newton's law. The model describes inflation and late time accelerated expansion with an effective cosmological constant for the inflationary epoch and small effective cosmological constant for the current accelerated phase.