Write the next sentence in this paragraph:

How to prepare for a high altitude hike
Begin training well in advance.
Plan the amount of training you will do based on the difficulty of your hike, and your current fitness level. If you are reasonably fit, and attempting a challenging hike, then you will probably want to schedule at least 5 months of training before your hike is scheduled.
If you are really out of shape, you may need to train for much, much longer. Remember that you can never start training too early, but you can start too late.