N, M = map(int, input().split())
D = [int(input()) for _ in range(M)]
D.sort()

ans = 10**18
for i in range(M - N + 1):
    # D[i] ~ D[i + N - 1] を拾う
    l = D[i]
    r = D[i + N - 1]
    if r <= 0:
        sub = abs(l)
    elif 0 <= l:
        sub = abs(r)
    else:
        sub = min(
            abs(l) + (r - l),
            abs(r) + (r - l)
        )
    if sub < ans:
        ans = sub
print(ans)