def solve():
    N, M = map(int, input().split())
    D = []

    for i in range(M):
        D.append(int(input()))

    D.sort()

    ans = 1e9

    for l in range(M):
        r = l + N - 1
        if r >= M:
            break
        if D[l] <= 0 and D[r] <= 0:
            ans = min(ans, -D[l])
        elif D[l] >= 0 and D[r] >= 0:
            ans = min(ans, D[r])
        else:
            ans = min(ans, min(-D[l] * 2 + D[r], -D[l] + D[r] * 2))
    print(ans)


if __name__ == '__main__':
    solve()