I lost one of my birth control pills what should I do?

It was one of the period pills. I have benn really consistant in taking my pills and I have been on them for a year and I have never missed a pill. I was taking the pill out the pack and my dad accidently bumped into me and I drop the pill in a vent and I couldn't get it. What should I do? Is not taking this pill going to affect my period? I know I need to use backup birth control (condoms) which I do anyways.