static int Flags(int[] a)
{
    var size = a.Length;
    if (size == 0)
    {
        return 0;
    }

    var peaks = new bool[size];
    var next = new int[size];

    for (int i = 1; i < size; i++)
    {
        var right = i + 1 < size ? a[i + 1] : 0;
        peaks[i] = a[i - 1] < a[i] && a[i] > right;
    }

    next[size - 1] = -1;
    for (int i = size - 2; i >= 0; i--)
    {
        next[i] = peaks[i] ? i : next[i + 1];
    }

    var result = 0;
    for (int i = 1; i * (i - 1) <= size; i++)
    {
        var pos = 0;
        var num = 0;
        while (pos < size && num < i)
        {
            pos = next[pos];
            if (pos == -1)
            {
                break;
            }
            num++;
            pos += i;
        }
        result = Math.Max(result, num);
    }

    return result;
}