## Description

Given a tree, calculate the average distance between two vertices in the tree. For example, the average distance between two vertices in the following tree is (d01 + d02 + d03 + d04 + d12 +d13 +d14 +d23 +d24 +d34)/10 = (6+3+7+9+9+13+15+10+12+2)/10 = 8.6.## Input

On the first line an integer t (1 <= t <= 100): the number of test cases. Then for each test case: * One line with an integer n (2 <= n <= 10 000): the number of nodes in the tree. The nodes are numbered from 0 to n - 1. * n - 1 lines, each with three integers a (0 <= a < n), b (0 <= b < n) and d (1 <= d <= 1 000). There is an edge between the nodes with numbers a and b of length d. The resulting graph will be a tree.## Output

For each testcase: * One line with the average distance between two vertices. This value should have either an absolute or a relative error of at most 10^(-3).## Sample Input

1 5 0 1 6 0 2 3 0 3 7 3 4 2## Sample Output

8.600## Source

Benelux Algorithm Programming Contest October 27, 2007