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#4951. 石头游戏

Estadísticas

Alice 和 Bob 将进行一场有 3 堆石子的游戏。他们轮流进行,每一回合,玩家必须选择一堆仍有石子的堆,并从中移除正整数个石子。谁移除了最后一堆中剩下的最后一颗石子,谁就获胜。Alice 先手。

第 $i$ 堆石子的数量是在范围 $[L_i, R_i]$ 内随机且均匀分布的。在双方都采取最优策略的情况下,Alice 获胜的概率是多少?

输入格式

输入包含一行 6 个整数,分别为 $L_1, R_1, L_2, R_2, L_3, R_3$。对于每个 $i$,满足 $1 \le L_i \le R_i \le 10^9$。

输出格式

输出一个整数,表示 Alice 获胜的概率对 $10^9 + 7$ 取模的结果。

可以证明答案可以表示为一个不可约分数 $\frac{p}{q}$,其中 $p$ 和 $q$ 是整数且 $q \not\equiv 0 \pmod{10^9 + 7}$,也就是说,我们感兴趣的是整数 $p \times q^{-1} \pmod{10^9 + 7}$。

样例

样例输入 1

3 3 4 4 5 5

样例输出 1

1

样例输入 2

4 4 8 8 12 12

样例输出 2

0

样例输入 3

1 10 1 10 1 10

样例输出 3

580000005

样例输入 4

5 15 2 9 35 42

样例输出 4

1

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