A question on Sorting by Comparision Counting

In TAOCP, Volume 3 - Sorting and Searching, Page Number -77, an
algorithm for Sorting by Comparision Counting is given. I understand
the algorithm. What I do not understand is Knuth has stated that the
running time of the program is 13N + 6A + 5B - 4;

This is the C++ snippet I am using

bool SortByComparisionCount()
{
	                        // I use 87 instead of 087 and 61 instead of
061
                                         int aKeys[]			= {503, 87,
512, 61,
						   908, 170, 897, 275,
						   653, 426, 154, 509,
						   612, 677, 765, 703};

	int aCountList[]	= {0, 0, 0, 0,
						   0, 0, 0, 0,
						   0, 0, 0, 0,
						   0, 0, 0, 0,};

	int aSortedList[]	= {0, 0, 0, 0,
						   0, 0, 0, 0,
						   0, 0, 0, 0};

	int aKeyCount		= 16;

	for(int i = aKeyCount - 1; i > 0; i--)
	{
		for(int j = i-1; j >= 0; j--)
		{
			if(aKeys[i] <= aKeys[j])
			{
				++aCountList[j];
			}
			else
			{
				++aCountList[i];
			}
		}
	}

	for( int j = 0; j < aKeyCount; j++)
	{
		aSortedList[aCountList[j]] = aKeys[j];
	}

	return true;
}


For me as a C++ programmer I will roughly abstract,
Running time = Number of times the inner loop is executed.

In this equation Knuth has given,
13N + 6A + 5B - 4
'N' I know.
Why 13 N?. 'A' I understand. 'B' I understand.
Why is this 13N + 6A + 5B - 4???

I really need to care about this equation as I proceed? Or My
assumption of
"Running time = Number of times the inner loop is executed" is fair
enough?

Please help.

PS: I understand that it is Out of Topic. But I feel that there is no
better place than comp.lang.c++ to discuss about programming. Please
bear with me.