t = int(input())
x, a = map(int, input().split())
y, b = map(int, input().split())
ans = float("inf")
for i in range(10**7):
  now = a * i
  tmp = x * i
  if now < t:
    tmp += t - now
  else:
    tmp += -((t - now) // b) * y
    tmp += (t - now) % b
  ans = min(ans, tmp)
print(ans)