#include <iostream>

 #include <vector>

 #include <algorithm>

 #include <queue>

 #include <stack>

 using namespace std;

 struct node {

     int data;

     struct node *left, *right;

     node() : data(), left(NULL), right(NULL) { }

     node(int d) : data(d), left(NULL), right(NULL) { }

 };

 void print(node *node) {

     if (!node) return;

     print(node->left);

     cout << node->data << " ";

     print(node->right);

 }

 bool balanced(node *root, int &height) {

     if (!root) return true;

     int l = ;

     int r = ;

     if (!balanced(root->left, l) || !balanced(root->right, r)) return false;

     if (l - r >=  || r - l >= ) return false;

     height = max(l, r) + ;

     return true;

 }

 int main() {

     struct node* root = new node();

     root->left = new node();

     root->right = new node();

     root->left->left = new node();

     root->left->right = new node();

     root->right->left = new node();

     root->left->left->left = new node();

     int height = ;

     if (balanced(root, height)) cout << "yes" << endl;

     else cout << "NO" << endl;

     return ;

 }