import java.util.*;

interface MyList{
 void convert(String[] a);
 void replace(int idx);	
 ArrayList<String> compact();
}

/*
Write the implementation of the InvalidStringException and the ArrayToList classes
Model strings for cut and paste:
I have added the string: {string} at the index: {index}
I have replaced the string: {string} with a null string
*/

public class Solution{
  
  public static void main(String[] args){
  
  Scanner sc = new Scanner(System.in);
  Random rand = new Random(0);

  int n = Integer.parseInt(sc.nextLine());
  String[] a = new String[n];

  for(int i = 0; i < n; i++)
  	a[i] = sc.nextLine();
  
  MyList obj = new ArrayToList();

  obj.convert(a);
  int x = rand.nextInt(n);
  for(int i = 0; i < x; i++)
  	obj.replace(rand.nextInt(n));


  ArrayList<String> s = obj.compact();
  


  for (int i = 0; i < s.size(); i++){
  	if(s.get(i).charAt(0) >= 97 && s.get(i).charAt(0) <= 122){
  	 try{
       throw new InvalidStringException("This is an invalid string");
  	 }
  	 catch(InvalidStringException e){System.out.println(e.getMessage());}	
  	}
  }


}
}