T = int(input())
X, A = map(int, input().split())
Y, B = map(int, input().split())
ans = 10 ** 15 + 1
tmp = 10 ** 15
y = max(-(T//B),0)
while ans > tmp:
    ans = tmp
    x = (T + B * y) // A
    d = (T + B * y) % A
    tmp = X * x + Y * y + d
    y += 1
print(ans)