n, m = map(int,input().split())
d = [int(input()) for j in range(m)]
if min(d) >= 0:
    print(d[n-1])
    exit()
if max(d) <= 0:
    print(d[-n])
    exit()

start = 0
end = n - 1
ans = 100000

while end < m:
    if d[start] <= 0 and d[end] >= 0:
        ans = min(ans, d[end]-d[start]-d[start], -d[start]+d[end]+d[end])
    elif d[start] < 0 and d[end] < 0:
        ans = min(ans, abs(d[start]))
    else:
        ans = min(ans, abs(d[end]))
    start += 1
    end += 1

print(ans)