1. 3x5 + some more 4's and 5's
2. 2x5 + 1x4 + other 4's
3. 1x5 + 1x4's + more 4's
4. 0x5 + 4x4's + more 4's
In the first case trade in 3x5's for 4x4's to reach n+1.
In the second case trade in 1x5 and 1x4 for 2x5's to reach n=1
In third case trade in 1x5 and 1x4 for 2x5's to reach n+1
In fourth case trade in 1x4 for 1x5 to reach n+1