package Others;

import java.util.*;

public class StackPostfixNotation {
 public static void main(String[] args) {
 Scanner scanner = new Scanner(System.in);
 String post = scanner.nextLine(); // Takes input with spaces in between eg. "1 21 +"
 System.out.println(postfixEvaluate(post));
 scanner.close();
 }

 // Evaluates the given postfix expression string and returns the result.
 public static int postfixEvaluate(String exp) {
 Stack<Integer> s = new Stack<Integer>();
 Scanner tokens = new Scanner(exp);

 while (tokens.hasNext()) {
 if (tokens.hasNextInt()) {
 s.push(tokens.nextInt()); // If int then push to stack
 } else { // else pop top two values and perform the operation
 int num2 = s.pop();
 int num1 = s.pop();
 String op = tokens.next();

 if (op.equals("+")) {
 s.push(num1 + num2);
 } else if (op.equals("-")) {
 s.push(num1 - num2);
 } else if (op.equals("*")) {
 s.push(num1 * num2);
 } else {
 s.push(num1 / num2);
 }

 // "+", "-", "*", "/"
 }
 }
 tokens.close();
 return s.pop();
 }
}