B = input()
N = input()
C = [input() for _ in xrange(N)]

def f(m):
	global B, N, C
	b = B
	res = 0
	for i in xrange(N):
		if C[i] >= m:
			res += C[i] - m
			b += C[i] - m
		else:
			res += m - C[i]
			b -= m - C[i]
	if b < 0: return 10 ** 15
	return res

l, r = -1, (sum(C) + B) / N + 1
while r - l > 1:
	m = (l + r) / 2
	if f(m + 1) - f(m) < 0:
		l = m
	else:
		r = m

print f(r)