let n = int (stdin.ReadLine())
let a = stdin.ReadLine().Split() |> Array.map int
let b = stdin.ReadLine().Split() |> Array.map int
let c = stdin.ReadLine().Split() |> Array.map int
Array.fold (fun (value, back) z -> if z = back + 1 then (b.[z - 1] + c.[back - 1] + value, z) else (b.[z - 1]+ value, z)) (0, -1) a |> fst |> printfn "%d"