Resolved Question: Which song is this? (need original song of that music)?

on the floor jennifer lopez (ft-pit bull)

when this song starts there is a piano music (don't know which
instrument was that exactly :P) (see the below video at 0:26-0:36) can
anyone tell me which song was that originally? its actually a very old
and famous song, since i am from India i hardly listen to pop music.
thanks in advance.

http://www.youtube.com/watch?v=t4H_Zoh7G5A

even the song starts with the same tune with the lyrics "Dance the
night away
Live your life and stay out on the floor "