Постфикс нотација

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


interface Stack<E>{
    public boolean isEmpty();
    public void clear();
    public void push(E x);
    public E pop();
    public E peek();
}

class Node<E>{
    E data;
    Node<E> next;

    Node(){
        data=null;
        next=null;
    }

    Node(E data,Node<E> next){
        this.data=data;
        this.next=next;
    }

    public E getData() {
        return data;
    }

}

class LinkedStack<E> implements Stack<E>{
    private Node<E> top;

    LinkedStack(){
        top=null;
    }

    public boolean isEmpty() {
        return top==null;
    }

    public E peek() {
        if(top!=null) return top.data;
        throw new NoSuchElementException();
    }

    public void clear() {
        top=null;
    }

    public E pop() {
        if(top!=null) {
            E popData=top.data;
            top=top.next;
            return popData;
        }
        throw new NoSuchElementException();
    }

    public void push(E x) {
        Node<E> newTop= new Node<E>(x,top);
        top=newTop;
    }

}



public class PostFixEvaluation{

    public static int postfiks(String[] exp) {

        LinkedStack<Integer> stack=new LinkedStack<>();

        for(int i=0;i<exp.length;i++) {
            if(Character.isDigit(exp[i].charAt(0))) {
                stack.push(Integer.parseInt(exp[i]));
            }
            if(exp[i].charAt(0)=='+') {
                int right=stack.pop();
                int left=stack.pop();
                int res=left+right;
                stack.push(res);
            }
            if(exp[i].charAt(0)=='-') {
                int right=stack.pop();
                int left=stack.pop();
                int res=left-right;
                stack.push(res);
            }
            if(exp[i].charAt(0)=='*') {
                int right=stack.pop();
                int left=stack.pop();
                int res=left*right;
                stack.push(res);
            }
            if(exp[i].charAt(0)=='/') {
                int right=stack.pop();
                int left=stack.pop();
                int res=left/right;
                stack.push(res);
            }
        }

        return stack.pop();
    }



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

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

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

       String[] argumenti=expression.split("\\s");
       System.out.println(postfiks(argumenti));
        br.close();

    }

}