import java.util.ArrayList;
 
// Implementing a stack is trivial using a dynamic array
// (which we implemented earlier).
public class Stack {
 
    ArrayList<Integer> stack = new ArrayList<Integer>();
 
    public Stack() {   
    }
 
    public void push(int n) {
        stack.add(n);
    }
 
    public int pop() {
        return stack.remove(stack.size() - 1);
    }
 
    public int size() {
        return stack.size();
    }
}