A deep mine's ventilation system is laid out as a binary tree of duct junctions. Each junction is either a sealed sensor with no children, or it splits into exactly two child ducts. Cold, dense air always wins at a merge point, so every junction with two children reports a temperature equal to the minimum of its two children's readings. You are given the full network of readings and must report the second-coldest distinct temperature that appears anywhere in the tree.

Input format

• Line 1: an integer n — the number of junctions (junction 1 is the mine's main outlet, i.e. the root).
• Each of the next n lines describes junction i (for i from 1 to n, in that order) as three integers val_i left_i right_i:
  • val_i is the temperature reading at junction i.
  • left_i and right_i are the 1-indexed junction numbers of its two children, or both 0 if junction i has no children.

Every junction has either exactly zero children or exactly two children. Whenever a junction has two children, its reading is guaranteed to equal the minimum of its two children's readings.

Output format

Print a single integer: the second smallest distinct reading in the whole network, or -1 if fewer than two distinct readings exist.

Constraints

• 1 <= n <= 25 (note that n is always odd, since every junction has 0 or 2 children).
• 0 <= val_i <= 2^31 - 1.
• left_i, right_i are either 0 or valid junction indices, forming a single tree rooted at junction 1 with no cycles.

5
2 2 3
2 0 0
5 4 5
5 0 0
7 0 0

5

3
2 2 3
2 0 0
2 0 0

-1