# -*- coding:utf-8 -*-

if __name__ == "__main__":
	b = input()
	n = input()
	C = []
	for i in xrange(n):
		C.append(input())
	inf = float("INF")
	ans = 10 **18
	l,r = -1,10**18
	while r - l > 2:
		lm,rm = (2 * l +r) / 3,(l + 2 * r) / 3
		if sum(lm - c for c in C) > b:
			r = lm
		elif sum(rm - c for c in C) > b:
			r = rm
		elif sum(abs(lm-c) for c in C) <= sum(abs(rm-c)for c in C):
			r = rm
		else:
			l = lm
	print sum(abs((r+l) / 2 - c)for c in C)