Enter the Giant Chasm cave in Route 13. Then turn left and go straight until you see the end of the cave on the left. Next, Go through Route 23 and when you enter Victory Road, you will see N and he will give you Waterfall. Also, Go through the badge checker. Then there is a Pokemon Center, heal your Pokemon if you need to. After that, there should be a door and enter through there and go through Victory Road until you get to the Pokemon League. Good Luck!