include

using namespace std;

class Node { public: int data; Node* next; };

class LinkedStack { private: Node* top; public: LinkedStack() { top = NULL; }

void push(int value) {
    Node* newNode = new Node();
    newNode->data = value;
    newNode->next = top;
    top = newNode;
}

void pop() {
    if (top == NULL) {
        cout << "Stack is empty." << endl;
    } else {
        Node* temp = top;
        top = top->next;
        delete temp;
    }
}

int peek() {
    if (top == NULL) {
        cout << "Stack is empty." << endl;
        return -1;
    } else {
        return top->data;
    }
}

bool isEmpty() {
    return top == NULL;
}

};

int main() { LinkedStack stack; stack.push(10); stack.push(20); stack.push(30); stack.push(40);

cout << "Top element: " << stack.peek() << endl;

stack.pop();
stack.pop();

cout << "Top element after popping twice: " << stack.peek() << endl;

if (stack.isEmpty()) {
    cout << "Stack is empty." << endl;
} else {
    cout << "Stack is not empty." << endl;
}

return 0;

}