#include<bits/stdc++.h>
using namespace std;

int size=1,counter,in;
int* tab = new int[1];

void alloc(int res){
  int* helptab = new int[counter];
  for(int i = 0;i < counter;i++)
    helptab[i] = tab[i];
  delete[] tab;
  tab = new int[res];
  for(int i = 0;i < counter;i++)
    tab[i] = helptab[i];
   delete[] helptab;
   size = res;
}

void pb(int x){
  if(counter == size)
    alloc(2*counter);

  tab[counter] = x;
  counter++;
}

void pop(){
  if(counter == 0){
    cout<<"No elements left, sorry!\n";
    return;
  }
  counter--;
  if(counter < size/4)
    alloc(size/2);
}

void t(int x){
  if(x<counter && x>=0)
  cout<<"The "<<x<<"-th element is "<<tab[x]<<"\n";
  else
  cout<<"This element doesn't exist\n";
}

int main() {
  cout<<"Welcome to probably the best vector in the universe!\nYour commands are as follows:\npb x = add x at the end\npop = delete the last element\nt x = check the x-th position(if it exists)\nexit = terminates the program\n";
  string comm = "a";
  while(comm != "exit"){
    cin>>comm;
    if(comm == "pb"){
      cin>>in;
      pb(in);
    }
    if(comm == "pop")
    pop();
    if(comm == "t"){
      cin>>in;
      t(in);
    }
  }
  cout<<"Farewell!\n";
  return 0;
}