func main()
	var _: [][]char :: cui@input().split(" ")
	var K: int :: _[0].toInt(&)
	var N: int :: _[1].toInt(&)
	var F: int :: _[2].toInt(&)
	do _ :: cui@input().split(" ")
	var ans: int :: K * N
	for i(0, F - 1)
		do ans :- _[i].toInt(&)
	end for
	do ans :: [ans, -1].max()
	do cui@print("\{ans}\n")
end func