#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cmath>
using namespace std;
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
int dfs(struct TreeNode *root)
{
int l,r;
if(root==NULL) return 0;
l=dfs(root->left);
if(l<0) return l;
r=dfs(root->right);
if(r<0) return r;
if(abs(l-r)>1) return -1;
return max(l,r)+1;
}
bool isBalanced(TreeNode *root)
{
return dfs(root) >=0? true:false;
}
int main()
{
printf("hello world\n");
}
