Auto comment: topic has been updated by ErnBeNQ (previous revision, new revision, compare).

why people aren't help??

I don't know if it's correct or not but think like this. At first, you need 12 sticks to make a cube. Now, the optimal way to place a second cube will be to share it with one face of the first cube. Hence, the number of sticks required will be 12 - 4 = 8. Now, For third cube, you have to place it with a face common with first or second cube, but make sure that it's perpendicular to the first two cubes. Here, number of sticks required will be 12 - 4 = 8. Now, for the fourth cube, there is already a place left to place with with two faces sharing between first and third (or second and third) cubes. Here the number of sticks required will be 12 - 4 - 4 + 1 = 5. Now just repeat this process.

It's probably getting the biggest perfect cube <= n and making a huge cube with these dimensions. Then you can place more matches on the borders of this huge cube to fill up the remaining unit cubes.