package main

import . "fmt"

func main() {
	var n int
	Scan(&n)
	st := []int{}
	for i := 0; i < n; i++ {
		var x int
		var s string
		Scan(&s)
		switch s {
			case "+":
				l := len(st)
				st[l-2] += st[l-1]
				st = st[:l-1]
			case "-":
				l := len(st)
				st[l-2] -= st[l-1]
				st = st[:l-1]
			default:
				Sscan(s, &x)
				st = append(st, x)
		}
	}
	Println(st[0])
}