City Bike Sharing

You are tasked with designing a bike-sharing system in a city. The city has `N` stations that are interconnected, and every station has a number of bikes available. The bike-sharing demand fluctuates over a day, and you need to determine the maximum number of bikes you can maintain in service during peak demand periods without exceeding limits on each station. Input: The first line contains an integer `N` (the number of stations). The next `N` lines each contain two integers: `C_i` (capacity of the station) and `D_i` (number of bikes currently demanded at that station). Output: Print a single integer: the maximum number of bikes that you can rent out without exceeding the capacities. Example: Input: 3 4 2 3 3 5 6 Output: 9