[infinity.]

@frank, don't worry about how long it takes to get tired. set small goals for periods of time first (run a half a mile, run a mile, run for 15 minutes, etc). you can stop during the run, but don't quit. i struggled with half miles when i started and would get the same cramps within very short amounts of time, it's a combination of bad dieting and being out of shape (more so out of shape), your body adjusts over time

the biggest running advice anyone can ever give is "shut up and run!"