Path Finding - Numeric Puzzle

This is a puzzle game which you connect path between start and goal point so as to minimize the total value.
Rule is simple, but you will use your brain more than you image. (So, this app will be use for brain training.)
The larger size is, the more difficult game is. (5x5, 9x9, 13x13)
Perforated versions are ready for each size.

By playing repeatedly, break your record!