B"A binary tree of n nodes is given. Nodes of the tree are numbered from 1 to n and the root is the node 1 . Each node can have no child, only one left child, only one right child, or both children. For convenience, let's denote l_u and r_u as the left and the right child of the node u respectively, l_u = 0 if u does not have the left child, and r_u = 0 if the node u does not have the right child. Each node has a string label, initially is a single character c_u . Let's define the string representation of the binary tree as the concatenation of the labels of the nodes in the in-order. Formally, let f(u) be the string representation of the tree rooted at the node u . f(u) is defined as follows: f(u) = begin{cases} texttt{<empty string>}, & text{if }u = 0; f(l_u) + c_u + f(r_u) & text{otherwise}, end{cases} where + denotes the string concatenation operation. This way, the string representation of the tree is f(1) . For each node, we can duplicate its label at most once, that is, assign c_u with c_u + c_u , but only if u is the root of the tree, or if its parent also has its label duplicated. You are given the tree and an integer k . What is the lexicographically smallest string representation of the tree, if we can duplicate labels of at most k nodes? A string a is lexicographically smaller than a string b if and only if one of the following holds: The first line contains two integers n and k ( 1 <= k <= n <= 2 cdot 10^5 ). The second line contains a string c of n lower-case English letters, where c_i is the initial label of the node i for 1 <= i <= n . Note that the given string c is not the initial string representation of the tree. The i -th of the next n lines contains two integers l_i and r_i ( 0 <= l_i, r_i <= n$$"...