APS_LAB4_Task1

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.NoSuchElementException;


interface Stack<E> {

    // Elementi na stekot se objekti od proizvolen tip.

    // Metodi za pristap:

    public boolean isEmpty();
    // Vrakja true ako i samo ako stekot e prazen.

    public E peek();
    // Go vrakja elementot na vrvot od stekot.

    // Metodi za transformacija:

    public void clear();
    // Go prazni stekot.

    public void push(E x);
    // Go dodava x na vrvot na stekot.

    public E pop();
    // Go otstranuva i vrakja elementot shto e na vrvot na stekot.
}

class ArrayStack<E> implements Stack<E> {

    // Stekot e pretstaven na sledniot nacin:
    //depth e dlabochinata na stekot, a
    // elems[0...depth-1] se negovite elementi.
    private E[] elems;
    private int depth;

    @SuppressWarnings("unchecked")
    public ArrayStack(int maxDepth) {
        // Konstrukcija na nov, prazen stek.
        elems = (E[]) new Object[maxDepth];
        depth = 0;
    }


    public boolean isEmpty() {
        // Vrakja true ako i samo ako stekot e prazen.
        return (depth == 0);
    }


    public E peek() {
        // Go vrakja elementot na vrvot od stekot.
        if (depth == 0)
            throw new NoSuchElementException();
        return elems[depth - 1];
    }


    public void clear() {
        // Go prazni stekot.
        for (int i = 0; i < depth; i++) elems[i] = null;
        depth = 0;
    }


    public void push(E x) {
        // Go dodava x na vrvot na stekot.
        elems[depth++] = x;
    }


    public E pop() {
        // Go otstranuva i vrakja elementot shto e na vrvot na stekot.
        if (depth == 0)
            throw new NoSuchElementException();
        E topmost = elems[--depth];
        elems[depth] = null;
        return topmost;
    }
}

public class PostFixEvaluation {
    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String expression = br.readLine();
        char exp[] = expression.toCharArray();


        br.close();

        System.out.println(evaluateExpression(exp));

    }

    private static int evaluateExpression(char[] s) {
        String expression = String.valueOf(s);
        String[] elements = expression.split("\\s+");

        ArrayStack<String> stack = new ArrayStack<>(elements.length);

        int result = 0;

        for (int i = 0; i < elements.length; i++) {
            if(!isOperator(elements[i])) stack.push(elements[i]);
            else {
                int number1 = Integer.parseInt(stack.pop());
                int number2 = Integer.parseInt(stack.pop());
                int calculatedValue = calculateTerm(number2, number1, elements[i]);
                stack.push(String.valueOf(calculatedValue));
                if(i == elements.length-1) result = Integer.parseInt(stack.pop());
            }
        }
        return result;
    }

    private static int calculateTerm(int number1, int number2, String operator) {
        if(operator.equals("+")) return number1 + number2;
        else if(operator.equals("-")) return number1 - number2;
        else if(operator.equals("*")) return number1 * number2;
        else  return number1 / number2;
    }

    private static boolean isOperator(String op) {
        return op.equals("+") || op.equals("-") || op.equals("*") || op.equals("/");
    }
}