hey this is Juan Valero 20 year old mexican athlete and runner, on september 14th im running my first marathon i want to do it under 3 hours, im doing it in a flat but gravalley course on sea level, just 3 weeks ago i ran my first half marathon and completed it in 1:30:25, it was mexico citys half, which is pretty high and has a lot of ascents, so if you got any breathing tips for me or any other running tips i would really preciete it. Also if anybody knows how hard would the gravalley course would make it? thanks for reading this!