I'm confused about how exactly should I compute a change for a transactions. Say, for a given address I have 4 unspent outputs containing 2 BTC each and I want to send 5 BTC to other address. Here's what I do: 1. Find 3 outputs needed so the total is 6 BTC 2. Now, what should be the change? 6-5=1 or 8-5=3?