import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		ArrayDeque<Integer> stack = new ArrayDeque<>();
		for (int i = 0; i < n; i++) {
		    String a = sc.next();
		    if (a.equals("+")) {
		        stack.push(stack.pop() + stack.pop());
		    } else if (a.equals("-")) {
		        stack.push(-stack.pop() + stack.pop());
		    } else {
		        stack.push(Integer.parseInt(a));
		    }
		}
		System.out.println(stack.pop());
	}
}