//User function Template for Java

class Solution

{

    //Function to check whether a Binary Tree is BST or not.

    int minimum(Node root) {

        if(root==null)

            return Integer.MAX_VALUE;

        int res = root.data;

        res = Math.min(res,minimum(root.left));

        res = Math.min(res,minimum(root.right));

        return res;

    }

    int maximum(Node root) {

        if(root==null)

            return Integer.MIN_VALUE;

        int res = root.data;

        res = Math.max(res,maximum(root.left));

        res = Math.max(res,maximum(root.right));

        return res;

    }

    boolean isBST(Node root) {

        if(root==null)

            return true;

        else if(root.left==null && root.right==null)

            return true;

        if(isBST(root.left)==false || isBST(root.right)==false)

            return false;

        int min = maximum(root.left);

        int max = minimum(root.right);

        if(min<root.data && root.data<max)

            return true;

        return false;

        // code here.

    }

}