java.lang.ClassNotFoundException: org.jivesoftware.smack.ConnectionConfiguration

Hello~! first I can't  write English well. I am sorry. I have to study hard everything.

I have start to learn Smack. so I have downloaded smack api in my computer and maked a small sample program

like this

import java.io.*;

import java.util.*;

import org.jivesoftware.smack.*;

import org.jivesoftware.smack.ConnectionConfiguration;

class SampleCode

{

public static void main(String[] args)

{

  System.out.println("Hello Instant Messaging!");

  ConnectionConfiguration connConfig = new ConnectionConfiguration("talk.google.com", 5222, "gmail.com");

  XMPPConnection connection = new XMPPConnection(connConfig);

  try

  {

   connection.connect();

   connection.login("my id", "password");

  }catch (Exception ex) {}

  Roster roster = connection.getRoster();

  Collection<RosterEntry> entries = roster.getEntries();

  for (RosterEntry entry : entries)

  {

   System.out.println(entry);

  }

}

}

and compiled but It is not working~ plz~ help me.

error message : java.lang.ClassNotFoundException: org.jivesoftware.smack.ConnectionConfiguration