def main():
    t = int(input())
    x, a = map(int, input().split())
    y, b = map(int, input().split())
    ans = 1 << 60
    for i in range((10 ** 7) + 2):
        z = a * i
        if z > t:
            j = -(-(z - t) // b)
            z -= b * j
        else:
            j = 0
        k = t - z
        tmp = i * x + j * y + k
        if tmp < ans: ans = tmp

    print(ans)



if __name__ == '__main__':
    main()