Snaking Numbers

Your playground is a square field filled with numbers from one to ...(depending on the chosen difficulty).

Goal:
Complete the snake and be fast. You have to find a path from the beginning to the end in as less time as possible.

Rules:
It is your task to complete the snake's path from the upper left corner to the lower right corner. On your way you'll cross many numbers, but you can pass one number just once. And every number has to be on your path. The order you choose to cross the numbers does not matter.