If you had HSA money deducted from your pay checks, do not enter any amount.
Your HSA contribution has already been reported in Box 12 of your W-2 with code W: Employer Contributions to Health Savings Account.
Despite the misleading name, code W reports both your and your employer's contribution. (If you think the name is confusing, think of it as just "Contributions to Health Savings Account".)
If you put $1,500 in your HSA during 2016, and your employer matched your contribution, your W-2's Box 12 should have the amount of $3,000 with a code W.
