n, m = map(int,input().split())
d_list = [int(input()) for i in range(m)]
sorted_d = sorted(d_list)

res = 30000

for i in range(m - n + 1):
    left = sorted_d[i]
    right = sorted_d[i + n - 1]
    cur_range = right - left
    
    cur_dis = min(abs(left), abs(right)) + cur_range
    
    res = min(cur_dis, res)

    
print(res)