t = read_line.to_i64
x, a = read_line.split.map(&.to_i64)
y, b = read_line.split.map(&.to_i64)
ans = 1i64 << 60
20000000.times do |yc|
  pos = -b * yc
  if pos <= t
    days = y * yc
    if x < a
      diff = t - pos
      days += diff // a * x + diff % a
    else
      days += t - pos
    end
    ans = {ans, days}.min
  end
end
puts ans