dont worry so much about cadence, just find a gear that is comfortable. being distracted by trying to count pedal strokes will be more dangerous than mashing. If you're feeling like you're pushing too hard into the pedals, you need to downshift. Machka makes a strong point about inexperienced riders mashing too hard but if you're wondering if you are mashing too hard, you are.
Your other option is to get a computer that measures cadence, if you really care that much. But I'd say get out there and get comfortable riding, learn what works for you before worrying about cadence.