import java.util.Stack;

public class App {
    public static void main(String[] args) throws Exception {
        Stack<Integer> stack = new Stack<>();
        stack.push(45);
        stack.push(27);
        stack.push(18);
        stack.push(31);

        System.out.println(stack.size());
        System.out.println(stack.pop());
        System.out.println(stack.size());
        System.out.println(stack.peek());
        System.out.println(stack.empty());
        System.out.println(stack.isEmpty());        
    }
}