import java.io.BufferedReader
import java.io.InputStream
import java.io.InputStreamReader
import java.io.PrintWriter
import java.util.*

fun PrintWriter.solve(sc: FastScanner) {
    val n = sc.nextInt()
    val stack = Stack<Int>()
    val a = sc.nextLine().split(" ")
    for (i in 0 until n) {
        if (a[i] == "+") {
            val n1 = stack.pop()
            val n2 = stack.pop()
            stack.push(n1 + n2)
        } else if (a[i] == "-") {
            val n1 = stack.pop()
            val n2 = stack.pop()
            stack.push(n2 - n1)
        } else {
            stack.push(a[i].toInt())
        }
    }
    println(stack.pop())
}

fun main() {
    val writer = PrintWriter(System.out, false)
    writer.solve(FastScanner(System.`in`))
    writer.flush()
}

class FastScanner(s: InputStream) {
    private var st = StringTokenizer("")
    private val br = BufferedReader(InputStreamReader(s))

    fun next(): String {
        while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine())

        return st.nextToken()
    }

    fun nextInt() = next().toInt()
    fun nextLong() = next().toLong()
    fun nextLine() = br.readLine()
    fun nextDouble() = next().toDouble()
    fun ready() = br.ready()
}