sum equaling a specific number

Occasional Visitor

First time here so be gentle lol. I remember doing this years ago, so I know it's possible. What I am trying to do is have a sum equal 3 or -3 always. Meaning if I add 10+2+5+9 I want it to =3.  Or 10+5-50+4 I want to =-3. We know those answers are wrong, but I don't care. I need a positive sum to always equal +3, and a negative sum to always equal -3. Can anyone help?