A, B, N, M = map(int, input().split())


# k 個作れるか？
def can(k: int) -> bool:
    def f(a, n, b, m):
        if a < k and b < k: return False
        if a < k: return f(b, m, a, n)

        assert a >= k
        extra_a = max(0, k-b) * n
        return a - extra_a >= k

    return f(A, N, B, M)


lo = 0
hi = max(A, B)
ans = lo
while lo <= hi:
    m = (lo + hi) // 2
    if can(m):
        ans = max(ans, m)
        lo = m + 1
    else:
        hi = m - 1

print(ans)