// No.1135 RPN
package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	// sc.Text()
	sc.Scan()
	A := strings.Fields(sc.Text())

	var stack [500]int
	sp := 0

	for _, s := range A {
		if s == "+" {
			sp--
			b := stack[sp]
			sp--
			a := stack[sp]

			stack[sp] = a + b
			sp++
		} else if s == "-" {
			sp--
			b := stack[sp]
			sp--
			a := stack[sp]

			stack[sp] = a - b
			sp++
		} else {
			n, _ := strconv.Atoi(s)
			stack[sp] = n
			sp++
		}
	}
	fmt.Println(stack[sp-1])
}