n, m = map(int, input().split())
D = [int(input()) for _ in range(m)]

D.sort()
ans = 10**18
for i in range(n - 1, m):
    if D[i - n + 1] <= 0 and D[i] >= 0:
        ans = min(ans, 2 * min(abs(D[i - n + 1]), D[i]) + max(abs(D[i - n + 1]), D[i]))
    elif D[i] <= 0:
        ans = min(ans, abs(D[i - n + 1]))
    else:
        ans = min(ans, D[i])
print(ans)