static long TapeEquilibrium(int[] a)
{
    long firstPart = 0;
    long secondPart = a.Sum(x => (long)x);
    long min = long.MaxValue;

    for (int i = 0; i < a.Length - 1; i++)
    {
        firstPart += i;
        secondPart -= i;
        var difference = Math.Abs(firstPart - secondPart);
        min = difference < min ? difference : min;
    }

    return min;
}