import java.util.* ;

import java.io.*;

/*******************************************************

Following is the BinaryTreeNode class structure

class BinaryTreeNode<T> {

T data;

BinaryTreeNode<T> left;

BinaryTreeNode<T> right;

public BinaryTreeNode(T data) {

this.data = data;

}

}

*******************************************************/

public class Solution

{

public static int postOrderSuccessor(BinaryTreeNode<Integer> root, int M)

{

if(root==null){

return -1;

}

ArrayList<Integer> arr = new ArrayList<>();

postOrder(root , arr);

for (int i = 0; i < arr.size(); i++) {

int n = arr.get(i);

if (n == M && i < arr.size() - 1) {

int ans = arr.get(i + 1);

return ans;

}

}

return -1;

}

public static void postOrder(BinaryTreeNode<Integer> root , ArrayList<Integer> arr){

if (root == null) {

return;

}

postOrder(root.left, arr);

postOrder(root.right, arr);

arr.add(root.data);

}

}