// you can also use imports, for example:
import java.util.*;

// you can use System.out.println for debugging purposes, e.g.
// System.out.println("this is a debug message");

public class Solution {
    private List<Integer> stack=new ArrayList<>();
    private ArrayList<Integer> indices = new ArrayList<>();
    private boolean transactionStart=false;
    public Solution() {
        // write your code in Java SE 8

    }

    public void push(int value) {
                this.stack.add(value);
    }

    public int top() {
        if(this.stack.size() > 0 ){
            return this.stack.get(this.stack.size()-1);
        }
        return 0;
    }

    public void pop() {
        if(this.stack.size() > 0 ) {
            this.stack.remove(this.stack.size()-1);
        }
    }

    public void begin() {
        this.indices.add(this.stack.size()-1);
        this.transactionStart = true;
   }

   public boolean rollback() {
       if(this.indices.size() > 0 ){
            this.stack = this.stack.subList(0,this.indices.get(this.indices.size()-1)+1);
             this.indices.remove(this.indices.size()-1);
            return true;
       }
       return false;
   }

    public boolean commit() {
        if(this.indices.size() > 0 ) {
            this.indices.remove(this.indices.size()-1);
            return true;
        }
        return false;
    }

    public static void test() {
        // Define your tests here
        Solution sol = new Solution();
        sol.push(42);
        sol.push(2);
        assert sol.top() == 2 : "top() should be 42";
    }
};