B,N =[int(input())for _ in range(2)]
C =[int(input())for _ in range(N)]
S =sum(C) +B
l = 0
r = S//N
def check(a):
    d = 0
    for i in C:
        d += abs(a-i)
    return d

while int(l+0.1) != int(r):
    x = (l*2+r)/3
    y = (l+r*2)/3
    if check(x) > check(y):
        l = (l*2+r)/3
    else:
        r = (l+r*2)/3
n =int(l)
print(min(check(n),check(n+1)))