t = int(input())
x, a = map(int, input().split())
y, b = map(int, input().split())
ans = 10 ** 18
for ca in range(2 * 10 ** 7 + 1):
    rest = ca * a - t
    r2 = 0 if rest < 0 else (rest + b - 1) // b * b
    ans = min(ans, ca * x + r2 - rest + r2 // b * y)
print(ans)