pick =. dyad define
	if. 0=#y do.
		x=0
	else.
		coin =. {. y
		newCoins =. }. y
		+/([:pick&newCoins x-coin*])"0 i.>:<.x%coin
	end.
)
problem31 =: 200 pick 200 100 50 20 10 5 2 1