# coding: utf-8
# Your code here!
gomi, num = map(int, input().split())
plus = [1000000]
minus = [-1000000]
for i in range(num):
    a = int(input())
    if a >= 0:
        plus.append(a)
    else:
        minus.append(a)
plus.sort()
minus.sort()
minus.reverse()
current = 0
count = 0
ans = 0
while(1):
    if abs(current - plus[0]) <= abs(current - minus[0]):
        ans += abs(current - plus[0])
        current = plus.pop(0)
        count += 1
    else:
        ans += abs(current - minus[0])
        current = minus.pop(0)
        count += 1
    if count >= gomi:
        break
print(ans)