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?
Ben owes 1 to Glen and Sven owes 4 to Ben, so Ben stands to get 3 drinks.
Glen owes 2 to Rhen and Ben owes 1 to Glen, so Glen stands to lose 1 drink.
Similar is the case with Rhen and Sven, Both stand to lose one drink.
So, minimum of three drinks need to be purchased.
Glen, Rhen and Sven each will purchase one drink and give to Ben.