import sys

x, a, y, b, l = list(map(lambda x: int(x), sys.stdin.readline().split()))

left = 1
right = (x * a + y * b + l - 1) // l + 1

while left + 1 < right:
    w = (left + right) // 2
    F = [[0] * (y + 1) for i in range(x + 1)]
    for k in range(x + 1):
        for p in range(y + 1):
            if k * a + p * b >= w:
                for i in range(x + 1 - k):
                    for j in range(y + 1 - p):
                        F[i + k][j + p] = max(F[i][j] + 1, F[i + k][j + p])
                break
        if a * k >= w:
            break
    if F[x][y] >= l:
        left = w
    else:
        right = w

print(left)