题目描述 Suppose that all the keys in a binary tree are distinct positive integers. Given the $postorder$ and $inorder$ traversal sequences, you are supposed to output the last number of the $preorder$ traversal sequence of the corresponding binary tree. 输入格式 Each input file contains one test case. For each case, the first line gives a positive integer $N$ ($\leq 50,000$), the total number of nodes in the binary tree. The second line gives the $postorder$ sequence and the third line gives the $inorder$ sequence. All the numbers in a line are separated by a space. 输出格式 For each test case, print in one line the last number of the $preorder$ traversal sequence of the corresponding binary tree. 输入样例 7 1 2 3 4 5 6 7 2 1 4 3 7 5 6 输出样例 5