Experiment duration

A PM asks how long an experiment must run. You need required_per_variant visitors in each of num_variants equally sized groups, and the site delivers daily_visitors eligible visitors per day (all of whom enter the experiment). The experiment runs whole days, so any partial final day rounds up. Compute total = required_per_variant * num_variants and return the smallest whole number of days d with d * daily_visitors >= total, which equals ceil(total / daily_visitors) = (total + daily_visitors - 1) / daily_visitors using integer division. All inputs are non-negative and daily_visitors >= 1. Example: required_per_variant = 5000, num_variants = 2, daily_visitors = 3000 returns 4.