import java.util.*;
import java.util.zip.*;
import java.util.List;
import java.util.regex.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
import javax.swing.table.*;
import java.io.*;
import java.net.*;
import java.lang.reflect.*;
import java.lang.ref.*;
import java.lang.management.*;
import java.security.*;
import java.security.spec.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.imageio.*;
import java.math.*;


class main {

public static void main(final String[] args) throws Exception {
  TreeSet<String> set = new TreeSet();
  set.add("pot");
  set.add("potash");
  System.out.println(containsPrefixOf(set, "pot"));
}

static boolean containsPrefixOf(TreeSet<String> set, String s) {
  if (set == null || s == null) return false;
  while (true) {
    String key = set.floor(s);
    
    if (key == null) return false; // s is in front of whole set => no prefix in there
    int n = lengthOfCommonPrefix(key, s);
    if (n == key.length()) return true; // found!
    s = s.substring(0, n); // shorten and try again
  }
}

static int lengthOfCommonPrefix(String a, String b) {
  int i = 0, n = Math.min(a.length(), b.length());
  while (i < n && a.charAt(i) == b.charAt(i))
    ++i;
  return i;
}}