Rain Barrel

The rain barrel fills day by day — when does it first overflow? 🌧️

You get the barrel's capacity and the rain collected each day. Print the first day (1-based) the running total reaches or passes capacity, or no overflow.

Example:

Input: capacity = 20, rain = [5, 8, 4, 9] Output: 4

The running total climbs 5, 13, 17, 26 — it first reaches or passes 20 on day 4.