static long ArrayMaximalAdjacentDifference(int[] a)
{
    long dif = 0;

    for (int i = 1; i < a.Length - 1; i++)
    {
        dif = Math.Max(dif, Math.Max(Math.Abs((long)a[i] - a[i - 1]), Math.Abs((long)a[i] - a[i + 1])));
    }

    return dif;
}