Separating Dates Using IF Function

Hello,

I'm trying to set up an IF function, I believe...I have a spreadsheet that lists dates back to 2013 as MM/DD/YYYY. I'm trying to create a formula that would read that date (specifically the year) and then assign a number to it. For example 2014 =1, 2015 = 2, etc. I'm new to the intricacies of Excel and don't know what I'm doing.