use pigeonhole principle to solve please: will upvote

A group of n agents all start at the same location and each one takes an m-walk on the line, where a m-walk is a sequence of exactly 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 > m+1, then some pair of agents finishes their walk at the same location.