This is a relatively standard Dynamic Programming problem. The key is to
 maintain the optimal funness that can be obtained for any particular smartness (in an array). It is important to also do this for negative 
smartness, since another cow could be added to make the smartness 
positive later. Start with no cows. It is impossible to make any non-zero 
smartness, and for zero smartness the optimal funness is zero. Now start 
adding cows one at a time. For each original smartness/funness 
combination, try adding this cow. This produces a new S/F combination. If 
this particular smartness has never been produced, or has been produced 
but with less funness, then overwrite the array entry with the new 
funness amount. Once you have added all the cows, check all the array 
entries for non-negative smartness and funness, and pick the one with the 
highest total.