Linkedlist to stack adapter

I/O:

push 10 push 20 push 5 push 8 push 2 push 4 push 11 top size pop top size pop top size pop top size pop top size pop top size pop top size pop quit

O/P:

11 7 11 4 6 4 2 5 2 8 4 8 5 3 5 20 2 20 10 1 10

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

public class LinkedList_To_Stack_Adapter {

    public static class LLToStackAdapter {
        LinkedList<Integer> list;

        public LLToStackAdapter() {
            list = new LinkedList<>();
        }

        // write your code here
        int size() {
            return list.size();
        }

        // write your code here
        void push(int val) {
            list.addFirst(val);
        }

        // write your code here
        int pop() {
            return list.removeFirst();
        }

        // write your code here
        int top() {
            return list.get(0);
        }
    }

    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        LLToStackAdapter st = new LLToStackAdapter();

        String str = br.readLine();
        while (str.equals("quit") == false) {
            if (str.startsWith("push")) {
                int val = Integer.parseInt(str.split(" ")[1]);
                st.push(val);
            } else if (str.startsWith("pop")) {
                int val = st.pop();
                if (val != -1) {
                    System.out.println(val);
                }
            } else if (str.startsWith("top")) {
                int val = st.top();
                if (val != -1) {
                    System.out.println(val);
                }
            } else if (str.startsWith("size")) {
                System.out.println(st.size());
            }
            str = br.readLine();
        }
    }
}