interface Set<A> {
  boolean contains(A x);
  Set<A> include(A x);
}

abstract class LinkedList<A> implements Set<A> {

  public abstract boolean contains(A x);
  
  public LinkedList<A> insert(A x) {
    if (contains(x)) return this;
    else return new NonEmptyList(x, this);
  }
  
  public Set<A> include(A x) {
    return insert(x);
  }
}

class EmptyList<A> extends LinkedList<A> {
  
  public boolean contains(A x) {
    return false;
  }
}

class NonEmptyList<A> extends LinkedList<A> {
  
  private A elem;
  private LinkedList<A> rest;
  
  public NonEmptyList(A elem, LinkedList<A> rest) {
    this.elem = elem;
    this.rest = rest;
  }
  
  public boolean contains(A x) {
    return ((Object)elem).equals((Object)x) || 
      rest.contains(x);
  }
}

public class TestForDuplicates {
  
  public static void main(String[] args) {
    Set<String> set = new EmptyList();
    for (int i = 1; i < args.length; i++)
      set = set.include(args[i]);
    System.out.println(set.contains(args[0]));
  }
}