T=int(input())
X,A=map(int,input().split())
Y,B=map(int,input().split())

def calc(na:int):
    x = A*na
    t=X*na
    if x <= T:
        return (T-x) + t
    d = x-T
    nb = (d+B-1)//B
    t += Y*nb
    x -= B*nb
    return t + (T-x)


low = 0
high = 10**12
ans = 10**20

while low<high:
    c1 = (low*2+high)//3
    c2 = (low+high*2)//3

    t1 = calc(c1)
    t2 = calc(c2)

    if t1<t2:
        if high==c2:break
        high = c2
        ans = min(ans, t1)
    else:
        if low==c1:break
        ans = min(ans, t2)
        low = c1

for i in range(10**7):
    t = calc(i)
    ans = min(ans, t)

print(ans)