t = int(input())
x,a = map(int,input().split())
y,b = map(int,input().split())
ans = 10**10

for i in range(10**7+5):
    now = a*i
    dif = max(now-t,0)
    j = (dif+b-1)//b
    # print(i,now,dif,j,now-j*b)
    now -= j*b
    ans = min(ans,i*x+j*y+t-now)
print(ans)