You are given a 0-indexed integer array stations of length n, where stations[i] represents the number of power stations in the ith city. Each power station can provide power to every city in a fixed range. In other words, if the range is denoted by r, then a power station at city i can provide power to all cities j such that |i - j| <= r and 0 <= i, j <= n - 1. The power of a city is the total number of power stations it is being provided power from. The government has sanctioned building k more power stations, each of which can be built in any city, and have the same range as the pre-existing ones. Given the two integers r and k, return the maximum possible minimum power of a city, if the additional power stations are built optimally. Note that you can build the k power stations in multiple cities.