open System
// 標準入力からスペース、タブ区切りでトークン列を読み込む
let stdinTokens = seq {
    while true do
        let line =  Console.ReadLine() 
        let tokens = line.Split([|' '; '\t'|], StringSplitOptions.RemoveEmptyEntries)
        yield! tokens
}
let readn n = stdinTokens |> Seq.take n |> List.ofSeq
let readInts n = readn n |> List.map int
let readInt () = readInts 1 |> List.head
let N = readInt()
let r1 = readInts N
let r2 = readInts N
let sum n = (r1 |> List.take n |> List.sum) + (r2 |> List.skip (n-1) |> List.sum)
seq{1..N} |> Seq.map sum |> Seq.max |> printfn "%d"