USE PIGEONHOLE PRINCIPLE TO SOLVE: A group of n agents all start at the same location and each one takes 'a 2m + 1', then

USE PIGEONHOLE PRINCIPLE TO SOLVE:

A group of n agents all start at the same location and each one takes 'a <= m-walk' on the line, where 'a <= m-walk' is a sequence of at most m steps and each step moves the agent one unit to the left or one unit to the right. (Different agents might take different walks.) Prove that, if 'n > 2m + 1', then some pair of agents finishes their walk at the same location.