A building's structural drawing is a binary tree, one level of the tree per storey going downward. The foundation is the deepest level. Its cornerstone is the left-most node on that deepest level. Report the value written on that cornerstone.
Input format
Line 1: an integer n, the number of tokens on the next line.
Line 2: n space-separated tokens describing a binary tree in level-order (breadth-first). The first token is the root's value. Reading left to right, keep a queue of already-created nodes; for each node taken from the front of the queue, the next two tokens are its left child then its right child, where the token null marks a missing child. Only non-null children are added to the queue. Trailing null tokens for absent children at the deepest level may be omitted. Every node value is an integer.
Output format
A single integer: the value of the left-most node on the deepest level.
Constraints
- 1 <= n <= 129
- The tree has at least 1 and at most 40 nodes.
- Each node value is an integer with -1000 <= value <= 1000.