|1.||Up Up Down Down Left Right Left Right B A|
The Konami code. This was originally used on the SNES to receive nine lives in Contra. Commonly people add start to the end of the code; however, this is not necessary it was just so people would un-pause their game.
If you're having trouble with Contra use the Konami code man, it's up up down down left right left right B A. It's that simple.