for (long l = 0, p = rlen + 1; l < p; l++, alen--, blen--, rlen--)
	{
		short r = n;
		short aa = (a[alen] >= '0' && a[alen] <= '9') ? (a[alen] - '0') : (a[alen] - 'A' + 10);
		short bb =
			(blen >= 0 ?
			((b[blen] >= '0' && b[blen] <= '9') ? (b[blen] - '0') : (b[blen] - 'A' + 10))
			: 0);
		if (aa >= bb)
		{
			r = aa - bb;
			res[rlen] = (r < 10) ? ('0' + r) : ('A' + r - 10);
		}
		else
		{
			long ll = alen;
			do
			{
				ll--;
				if (a[ll] == '0')
					a[ll] = (n < 11) ? ('0' + n - 1) : ('A' + n - 10 - 1);
			}
			while (a[ll] == '0');
			a[ll] =
			(n < 11) ?
			(a[ll] - 1)
			: ((a[ll] == 'A') ? '9' : (a[ll] - 1));
			aa = (n < 11) ? (n + aa) : (10 + aa);
			r = aa - bb;
			res[rlen] = (r < 10) ? ('0' + r) : ('A' + r - 10);
		}
	}