/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        
        if(root==NULL) return 0;

        int left = maxDepth( root->left);
        int right = maxDepth( root->right);


        return (left>right? left:right) + 1;

    }
};