import java.util.Scanner;
import java.util.Stack;


public class HelloWorld {
		public static void main (String[] args) {
			Scanner sc = new Scanner(System.in);
			int n = Integer.parseInt(sc.nextLine());
			String[] strs = sc.nextLine().split(" ");
			sc.close();

			Stack<Integer> stack = new Stack<Integer>();
			for (String str : strs) {
				if (str.equals("+")) {
					stack.push(stack.pop() + stack.pop());
				}
				else if (str.equals("-")) {
					stack.push(-stack.pop() + stack.pop());
				}
				else {
					stack.push(Integer.parseInt(str));
				}
			}
			System.out.println(stack.pop());


	}
}