a, b, c = io.read("*n", "*n", "*n")
a = a * (b - c)
d, e = io.read("*n", "*n")
v = 1 <= a and d or 0
p = d
for i = 2, a do
  if i % 10 == 0 then
    if e <= p then
      p = p - e
    end
  end
  v = v + p
end
print(v)