let n = stdin.ReadLine() |> int
let a = stdin.ReadLine().Split() |> Array.toList

let canCalc n1 n2 op =
    if n1 = "+" || n1 = "-" then
        false
    elif n2 = "+" || n2 = "-" then
        false
    elif op <> "+" && op <> "-" then
        false
    else
        true

let rec roop (xs: string list) ys =
    if xs.Length < 3 then
       let tmp = List.rev xs @ ys
       if tmp.Length = 1 then
           // 戻り値
           tmp
       else
           roop (List.rev tmp) []
    else
        let x1 :: x2 :: x3 :: rest = xs
        if canCalc x1 x2 x3 then
            if x3 = "+" then
                let y = int x1 + int x2 |> string
                roop rest (y :: ys)
            else
                let y = int x1 - int x2 |> string
                roop rest (y :: ys)
        else
            roop (List.tail xs) (x1 :: ys)

roop a []
|> List.head
|> printfn "%s"