open System
open System.Collections.Generic

[<AutoOpen>]
module Cin =
    let read f = stdin.ReadLine() |> f
    let reada f = stdin.ReadLine().Split() |> Array.map f

    let readInts() =
        read string
        |> Seq.toArray
        |> Array.map (fun x -> Convert.ToInt32(x.ToString()))

module Util =
    let strRev s =
        s
        |> Seq.rev
        |> Seq.map string
        |> String.concat ""

[<EntryPoint>]
let main _ =
    let N = read int
    let AB = Array.zeroCreate (N - 1)
    for i in 0 .. N - 2 do
        AB.[i] <- reada int

    let asum = AB |> Array.sumBy (fun ab -> ab.[0])
    let bsum = AB |> Array.sumBy (fun ab -> ab.[1])
    let diff = asum - bsum
    let lim = asum
    let ans = lim - diff + 1
    printfn "%d" ans
    0 // return an integer exit code