A tree is said to be balanced if, for any of its vertices, the heights of the left and right subtrees for that vertex differ by no more than 1.
Input
A sequence of integers ending in zero is entered. Zero itself is not included in the sequence. Build a tree corresponding to the given sequence.
Output
Determine if the tree is balanced, output the word
YES or
NO.
Examples
| # |
Input |
Output |
| 1 |
7 3 2 1 9 5 4 6 8 0
|
YES
|