B = input()
N = input()
C = [input() for i in range(N)]


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

lb = 0
ub = (sum(C) + B) / N
while ub - lb > 2:
    lm = (lb*2+ub)/3
    um = (lb+ub*2)/3
    if sim(lm) < sim(um):
        ub = um
    else:
        lb = lm
print(min(sim(ub), sim(lb), sim((ub+lb)/2)))