AC

import java.util.ArrayList;
import java.util.Scanner;
import java.util.Stack;
public class Main {
	public static void main(String[] args) {
		ArrayList<Integer> inputs = new ArrayList<Integer>();
		Scanner in = new Scanner(System.in);
		String line = in.nextLine();
		if(line != null && ! line.isEmpty()) {
			int res = resolve(line.trim());
			System.out.println(String.valueOf(res));
		}
	}
	// write your code here
	public static int resolve(String expr) {
		Stack<Integer> stack = new Stack<>();
		String[] split = expr.split("\\s+");
		for (int i = 0; i < split.length; i ++) {
			if(split[i].equals("^")) {
				if(stack.size() < 1) return - 1;
				stack.push(stack.pop() + 1);
			} else if(split[i].equals("+")) {
				if(stack.size() < 2) return - 1;
				stack.push(stack.pop() + stack.pop());
			} else if(split[i].equals("*")) {
				if(stack.size() < 2) return - 1;
				stack.push(stack.pop() * stack.pop());
			} else {
				if(stack.size() > 16) return - 2;
				stack.push(Integer.parseInt(split[i]));
			}
		}
		return stack.pop();
	}
}