a, b, c, d, e = gets.split.map(&:to_i)

human_cnt = b - c
ame = human_cnt * a

price = 0

pre = 0
cur = 0

#p ame
#p d

ame.times do |i|
	if (i == 0) then 
		cur = d
	elsif ((i+1) % 10 != 0) then
		cur = pre
	elsif (e <= pre) then 
		cur = pre - e
	else cur = pre
	end
	#p e
	price += cur
	pre = cur
end

p price