b = input()
n = input()
c = [input() for i in range(n)]
lb = 0
ub = (sum(c) + b) / n


def sim(x):
    return sum(abs(y - x) for y in c)


for i in range(40):
    m = lb + (ub - lb) / 2
    if sim(lb) < sim(ub):
        ub = m
    else:
        lb = m
print(min(sim(lb), sim(ub)))