Chain for 2006 Madone 5.2 SL

I could use some help with the chain selection for my bike. The current chain has Shimano Ultegra CN-6600 stamped on it, but when I went to buy a chain, the box shows that this chain comes in different lengths. Can anyone help me figure out which to get? The choices are 114L, 116L, and 118L.

Appreciate any help!