A, B, C, D, E = gets.split.map(&:to_i)

def f(m)
  total = x = 0

  1.upto((B - C) * A) do |i|
    if i == 1
      total += (x = D)
    elsif i % 10 != 0
      total += x
    else
      if E <= x
        total += (x = [0, x - E].max)
      else
        total += x
      end
    end
  end

  total <= m
end

ok = 10 ** 18
ng = -1

while (ok - ng).abs >= 2
  x = (ok + ng) / 2

  if f(x)
    ok = x
  else
    ng = x
  end
end

puts ok