#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

struct Node {
  int data;
  struct Node *ptr;
};

struct Node *top = NULL;

void push(int v) {
  struct Node *new = (struct Node *)malloc(sizeof(struct Node));
  new->data = v;
  new->ptr = top;
  top = new;
}

int pop() {
  struct Node *temp = top;
  int v = temp->data;
  top = temp->ptr;

  free(temp);
  return v;
}
int peek() {
  if (top == NULL) {
    printf("Stack empty\n");
    return -1;
  }
  return top->data;
}

void display() {
  struct Node *temp = top;
  printf("Stack: ");
  while (temp != NULL) {
    printf("%d ", temp->data);
    temp = temp->ptr;
  }
  printf("\n");
}
int main() {
  push(10);
  push(20);
  push(30);
  display();

  printf("Popped: %d\n", pop());
  display();

  printf("Top: %d\n", peek());
}