Starved for Seating

You're the manager of a football stadium, and it's now time to decide whether to upgrade it or not. There are $N$ football teams. You know that the $i$-th team has $A_i$ fans. Each person is a fan of exactly one team, so the total number of people is $(A_1 + \ldots + A_N)$. It is guaranteed that each $A_i$ is an **even integer**. When a match between teams $X$ and $Y$ ($X \ne Y$) happens in t