 " S & M " is an uptempo hi @-@ NRG @-@ Eurodance song that lasts four minutes and three seconds . The song is composed in the key of E @-@ flat minor using common time and a moderate dance tempo of 128 beats per minute . Instrumentation is provided by synthesizers , a keyboard and a guitar . Chris Ryan of MTV described the song as a " steady @-@ rocking dance track , with ominous , snarling keyboard sounds . " 
