class Main {
  public static void main(String[] args) {
    System.out.println("Hello world!");
   
   /* *public boolean isSymmetric(TreeNode root) {
      if (root == null)
          return true;
      //从两个子节点开始判断
      return isSymmetricHelper(root.left, root.right);
  }
  
  public boolean isSymmetricHelper(TreeNode left, TreeNode right) {
      //如果左右子节点都为空，说明当前节点是叶子节点，返回true
      if (left == null && right == null)
          return true;
      //如果当前节点只有一个子节点或者有两个子节点，但两个子节点的值不相同，直接返回false
      if (left == null || right == null || left.val != right.val)
          return false;
      //然后左子节点的左子节点和右子节点的右子节点比较，左子节点的右子节点和右子节点的左子节点比较
      return isSymmetricHelper(left.left, right.right) && isSymmetricHelper(left.right, right.left);
  }*/
  for(int i=0;i<100;i++){
    System.out.println("Hello world!");
    if(i>8){
      return;
    }
  }
  
  }
}