import java.util.ArrayList;

class EmptyStackException extends IndexOutOfBoundsException {

public EmptyStackException() {

super("Stack is empty.");

}

}

class Stack<T> {

private ArrayList<T> list;

public Stack() {

this.list = new ArrayList<T>();

}

public void push(T item) {

this.list.add(item);

}

public T pop() {

if (this.size() == 0) {

throw new EmptyStackException();

}

return this.list.remove(this.size() - 1);

}

public T peek() {

if (this.size() == 0) {

throw new EmptyStackException();

}

return this.list.get(0);

}

public boolean isEmpty() {

return this.size() == 0;

}

public int size() {

return this.list.size();

}

}