def f(t):
    v = (t + B - 1)//B * Y
    t -= (t + B - 1)//B * B
    return v + abs(t)

T = int(input())
X, A = map(int, input().split())
Y, B = map(int, input().split())
ans = 10 ** 18
if T >= 0:
    ans = T//A * X + T - T//A * A
    ans2 = (T + A - 1)//A * X
    T -= (T + A - 1)//A * A
    ans2 += f(-T)
    print(min(ans, ans2))
else:
    print(f(-T))