T = int(input())
X,A = map(int, input().split())
Y,B = map(int, input().split())
ans = 10**20
for y in range(10**7+10):
    day = -y*B
    if T>=day:
        x = (T-day)//A
        ans = min(ans,y*Y+(T-day),y*Y+x*X+abs(T-(y*A-x*B)))
print(ans)