Four people are in a bar.
Ben owes Glen a drink. Glen owes Rhen two drinks. Rhen owes Sven three drinks. Sven owes Ben four drinks.
To settle up, what is the minimum number of drinks that need to be bought by who for whom?
OK, not really.
4. 1 per person.
Ben buys Glen a drink. Glen then gives that drink, plus one he has purchased, to Rhen. Rhen uses those two and purchases a third to pay off Sven. Sven can then take those three and buy his own to give all four to Ben and therefore pay off his debt.