CF1556A.A Variety of Operations

William has two numbers $a$ and $b$ initially both equal to zero. William mastered performing three different operations with them quickly. Before performing each operation some positive integer $k$ is picked, which is then used to perform one of the following operations: (note, that for each operation you can choose a new positive integer $k$)

1. add number $k$ to both $a$ and $b$, or
2. add number $k$ to $a$ and subtract $k$ from $b$, or
3. add number $k$ to $b$ and subtract $k$ from $a$.

Note that after performing operations, numbers $a$ and $b$ may become negative as well.

William wants to find out the minimal number of operations he would have to perform to make $a$ equal to his favorite number $c$ and $b$ equal to his second favorite number $d$.

威廉最初有两个数 $a$ 和 $b$，其值均为 $0$。威廉已熟练掌握对这两个数执行以下三种不同操作：每次执行操作前，需先选定一个正整数 $k$，然后用该 $k$ 执行以下三种操作之一（注意：每次操作均可重新选择一个新的正整数 $k$）：

1. 将数 $k$ 同时加到 $a$ 和 $b$ 上；
2. 将数 $k$ 加到 $a$ 上，同时从 $b$ 中减去 $k$；
3. 将数 $k$ 加到 $b$ 上，同时从 $a$ 中减去 $k$。

注意：执行操作后，$a$ 和 $b$ 的值可能变为负数。

威廉希望知道：为使 $a$ 等于他最喜爱的数 $c$、$b$ 等于他第二喜爱的数 $d$，他至少需要执行多少次操作？

Each test contains multiple test cases. The first line contains the number of test cases $t$ ($1 \le t \le 10^4$). Description of the test cases follows.

The only line of each test case contains two integers $c$ and $d$ $(0 \le c, d \le 10^9)$, which are William's favorite numbers and which he wants $a$ and $b$ to be transformed into.

每个测试包含多个测试用例。第一行包含测试用例的数量 $t$（$1 \le t \le 10^4$）。随后是测试用例的描述。

每个测试用例仅有一行，包含两个整数 $c$ 和 $d$（$0 \le c, d \le 10^9$），它们是 William 最喜欢的数字，他希望将 $a$ 和 $b$ 变换为这两个数字。

For each test case output a single number, which is the minimal number of operations which William would have to perform to make $a$ equal to $c$ and $b$ equal to $d$, or $-1$ if it is impossible to achieve this using the described operations.

对于每个测试用例，输出一个整数，表示 William 需要执行的最少操作次数，使得 $a$ 等于 $c$ 且 $b$ 等于 $d$；如果无法通过所描述的操作实现该目标，则输出 $-1$。

Let us demonstrate one of the suboptimal ways of getting a pair $(3, 5)$:

• Using an operation of the first type with $k=1$, the current pair would be equal to $(1, 1)$.
• Using an operation of the third type with $k=8$, the current pair would be equal to $(-7, 9)$.
• Using an operation of the second type with $k=7$, the current pair would be equal to $(0, 2)$.
• Using an operation of the first type with $k=3$, the current pair would be equal to $(3, 5)$.

让我们演示一种得到数对 $(3, 5)$ 的非最优方法：

• 使用第一类操作，取 $k=1$，当前数对变为 $(1, 1)$。
• 使用第三类操作，取 $k=8$，当前数对变为 $(-7, 9)$。
• 使用第二类操作，取 $k=7$，当前数对变为 $(0, 2)$。
• 使用第一类操作，取 $k=3$，当前数对变为 $(3, 5)$。