stack.cpp

#include<iostream>
#include<string.h>
#include<stack>
using namespace std;
stack<int> s;

int main()
{
  int size,n;
  char op[10];
  cin >> size;
  for (int i = 0; i < size; i++)
  {
    cin >> op;
    if (!strcmp(op,"push"))
    {
      cin >> n;
      s.push(n);
    }

    if (!strcmp(op,"pop"))
    {
      if (!s.empty())
      {
        cout << s.top() << endl;
        s.pop();
      }
      else cout << -1 << endl;
      
    }
    
    if (!strcmp(op,"top"))
    {
      if (!s.empty())
      {
        cout << s.top() << endl;
      } else cout << -1 << endl;
      
    }

    if (!strcmp(op,"size"))
    {
      cout << s.size() << endl;
    } 

    if (!strcmp(op,"empty"))
    {
      if (!s.empty())
      {
        cout << 0 << endl;
      } else cout << 1 << endl;
      
    }
  }
  
}