import math

def min_len(pos, Ds, N):
    length = max([math.fabs(i) for i in Ds])
    next_i = 0
    for i in range(len(Ds)):
        tmp_length = math.fabs(pos - Ds[i])
        if length > tmp_length:
            length = tmp_length
            next_i = i
    if N == 1:
        return int(length)
    next_pos = Ds[next_i]
    Ds.pop(next_i)
    return int(length) + min_len(next_pos, Ds, N-1)
            
str_N, str_M = input().split(" ")
N = int(str_N)
M = int(str_M)
Ds = []
for i in range(M):
    Ds.append(int(input()))

print(min_len(0, Ds, N))