Quiz

I was told that I am setting a puzzle. Okay. It's a fairly standard puzzle: you need to swap the numbers 4 and 5. Obviously, the numbers can only be moved to an empty cell, and the cell where the number was before becomes empty. But I don't need the solution to this problem. I am interested in the minimum number of moves required to solve this puzzle. A proof is desirable, but I think I won't require it (unless those who answer start solving the puzzle by brute force, then a proof will be needed).