I repaid a military reenlistment bonus from 2008 in the amount of $4576.72 using an installment repayment agreement with the Defense Finance and Accounting Office @ 1% interest

I received the reenlistment bonus in 2008, retired in 2010 and received a letter in 2012 that I needed to repay a portion.  Repayment was monthly installments from 2012 to 2016. I was allowed to keep half my bonus for the time served and then pay back the $4576.72 for the part of the enlistment I didn't stay for because I retired. How do I claim the 4576.72 this year as a deduction?